Only include opensslconf.h once

Fixes a pyca cryptography test failure.

[extended tests]

Reviewed-by: Richard Levitte <levitte@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/7839)

Remove the cast from the definition of OPENSSL_VERSION_NUMBER

If a cast is included in the definition it cannot be used in preprocessor
expressions, e.g. "#if OPENSSL_VERSION_NUMBER > 0x10000000L"

[extended tests]

Reviewed-by: Richard Levitte <levitte@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/7839)

Doc: fix reference to deprecated methods.

Reviewed-by: Paul Yang <yang.yang@baishancloud.com>
Reviewed-by: Paul Dale <paul.dale@oracle.com>
Reviewed-by: Matthias St. Pierre <Matthias.St.Pierre@ncp-e.com>
(Merged from https://github.com/openssl/openssl/pull/7705)

curve25519.c: improve formula alignment

Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/7750)

curve25519.c: reformat code to follow coding guidelines

Fixes #7698

Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/7750)

Remaining boilerplate change in doc/man3/OpenSSL_version.pod

Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/7838)

Following the license change, modify the boilerplates in include/ and crypto/include/

Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/7770)

Following the license change, modify the boilerplates in last few

[skip ci]

Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/7836)

Following the license change, modify the boilerplates in external/

[skip ci]

Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/7835)

Following the license change, modify the boilerplates in demos/

[skip ci]

Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/7834)

Following the license change, modify the boilerplates in fuzz/

[skip ci]

Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/7833)

Following the license change, modify the boilerplates in engines/

[skip ci]

Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/7832)

Following the license change, modify the boilerplates in doc/man7/

[skip ci]

Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/7831)

Following the license change, modify the boilerplates in doc/man5/

[skip ci]

Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/7830)

Following the license change, modify the boilerplates in doc/man3/

[skip ci]

Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/7829)

Following the license change, modify the boilerplates in doc/man1/

[skip ci]

Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/7828)

Following the license change, modify the boilerplates in crypto/

[skip ci]

Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/7827)

Following the license change, modify the boilerplates in crypto/ui/

[skip ci]

Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/7826)

Following the license change, modify the boilerplates in crypto/x509v3/

[skip ci]

Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/7825)

Following the license change, modify the boilerplates in crypto/x509/

[skip ci]

Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/7824)

Following the license change, modify the boilerplates in crypto/whrlpool/

[skip ci]

Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/7823)

Following the license change, modify the boilerplates in crypto/ts/

[skip ci]

Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/7822)

Following the license change, modify the boilerplates in crypto/store/

[skip ci]

Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/7821)

Following the license change, modify the boilerplates in crypto/stack/

[skip ci]

Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/7820)

Following the license change, modify the boilerplates in crypto/srp/

[skip ci]

Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/7819)

Following the license change, modify the boilerplates in crypto/smN/

[skip ci]

Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/7818)

Following the license change, modify the boilerplates in crypto/siphash/

[skip ci]

Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/7817)

Following the license change, modify the boilerplates in crypto/sha/

[skip ci]

Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/7816)

Following the license change, modify the boilerplates in crypto/seed/

[skip ci]

Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/7815)

Following the license change, modify the boilerplates in crypto/rsa/

[skip ci]

Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/7814)

Following the license change, modify the boilerplates in crypto/ripemd/

[skip ci]

Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/7813)

Following the license change, modify the boilerplates in crypto/rcN/

[skip ci]

Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/7812)

Following the license change, modify the boilerplates in crypto/rand/

[skip ci]

Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/7811)

Following the license change, modify the boilerplates in crypto/poly1305/

[skip ci]

Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/7810)

Following the license change, modify the boilerplates in crypto/pkcs7/

[skip ci]

Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/7809)

Following the license change, modify the boilerplates in crypto/pkcs12/

[skip ci]

Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/7808)

Following the license change, modify the boilerplates in crypto/perlasm/

[skip ci]

Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/7807)

Following the license change, modify the boilerplates in crypto/pem/

[skip ci]

Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/7806)

Following the license change, modify the boilerplates in crypto/ocsp/

[skip ci]

Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/7805)

Following the license change, modify the boilerplates in crypto/objects/

[skip ci]

Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/7804)

Following the license change, modify the boilerplates in crypto/modes/

[skip ci]

Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/7803)

Following the license change, modify the boilerplates in crypto/mdc2/

[skip ci]

Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/7802)

Following the license change, modify the boilerplates in crypto/mdN/

[skip ci]

Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/7801)

Following the license change, modify the boilerplates in crypto/lhash/

[skip ci]

Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/7800)

Following the license change, modify the boilerplates in crypto/hmac/

[skip ci]

Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/7799)

Following the license change, modify the boilerplates in crypto/gmac/

[skip ci]

Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/7798)

Following the license change, modify the boilerplates in crypto/kmac/

[skip ci]

Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/7797)

Following the license change, modify the boilerplates in crypto/kdf/

[skip ci]

Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/7796)

Following the license change, modify the boilerplates in crypto/idea/

[skip ci]

Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/7795)

Following the license change, modify the boilerplates in crypto/evp/

[skip ci]

Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/7794)

Following the license change, modify the boilerplates in crypto/err/

[skip ci]

Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/7793)

Following the license change, modify the boilerplates in crypto/engine/

[skip ci]

Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/7792)

Following the license change, modify the boilerplates in crypto/ec/

[skip ci]

Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/7791)

Following the license change, modify the boilerplates in crypto/dso/

[skip ci]

Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/7790)

Following the license change, modify the boilerplates in crypto/dsa/

[skip ci]

Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/7789)

Following the license change, modify the boilerplates in crypto/dh/

[skip ci]

Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/7788)

Following the license change, modify the boilerplates in crypto/des/

[skip ci]

Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/7787)

Following the license change, modify the boilerplates in crypto/ct/

[skip ci]

Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/7786)

Following the license change, modify the boilerplates in crypto/conf/

[skip ci]

Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/7785)

Following the license change, modify the boilerplates in crypto/comp/

[skip ci]

Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/7784)

Following the license change, modify the boilerplates in crypto/cms/

[skip ci]

Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/7783)

Following the license change, modify the boilerplates in crypto/cmac/

[skip ci]

Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/7782)

Following the license change, modify the boilerplates in crypto/chacha/

[skip ci]

Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/7781)

Following the license change, modify the boilerplates in crypto/cast/

[skip ci]

Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/7780)

Following the license change, modify the boilerplates in crypto/camellia/

[skip ci]

Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/7779)

Following the license change, modify the boilerplates in crypto/buffer/

[skip ci]

Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/7778)

Following the license change, modify the boilerplates in crypto/bn/

[skip ci]

Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/7777)

Following the license change, modify the boilerplates in crypto/blake2/

Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/7776)

Following the license change, modify the boilerplates in crypto/bio/

Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/7775)

Following the license change, modify the boilerplates in crypto/bf/

Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/7774)

Following the license change, modify the boilerplates in crypto/async/

Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/7773)

Following the license change, modify the boilerplates in crypto/asn1/

Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/7772)

Following the license change, modify the boilerplates in crypto/aes/

Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/7771)

Following the license change, modify the boilerplates in ms/

Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/7769)

Following the license change, modify the boilerplates in ssl/

Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/7768)

Following the license change, modify the boilerplates in test/

Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/7767)

Following the license change, modify the boilerplates in util/, tools/

Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/7766)

Following the license change, modify the boilerplates in apps/

Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/7765)

Change license to the Apache License v2.0

This applies to the 'master' git branch and OpenSSL version 3.0.0 and
up.  Pre-3.0.0 versions retain the previous license.

The boilerplate will change in increments after this change.

Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/7764)

License: change any non-boilerplate comment referring to "OpenSSL license"

Make it just say "the License", which refers back to the standard
boilerplate.

Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/7764)

Refactor the computation of API version limits

Previously, the API version limit was indicated with a numeric version
number.  This was "natural" in the pre-3.0.0 because the version was
this simple number.

With 3.0.0, the version is divided into three separate numbers, and
it's only the major number that counts, but we still need to be able
to support pre-3.0.0 version limits.

Therefore, we allow OPENSSL_API_COMPAT to be defined with a pre-3.0.0
style numeric version number or with a simple major number, i.e. can
be defined like this for any application:

    -D OPENSSL_API_COMPAT=0x10100000L
    -D OPENSSL_API_COMPAT=3

Since the pre-3.0.0 numerical version numbers are high, it's easy to
distinguish between a simple major number and a pre-3.0.0 numerical
version number and to thereby support both forms at the same time.

Internally, we define the following macros depending on the value of
OPENSSL_API_COMPAT:

    OPENSSL_API_0_9_8
    OPENSSL_API_1_0_0
    OPENSSL_API_1_1_0
    OPENSSL_API_3

They indicate that functions marked for deprecation in the
corresponding major release shall not be built if defined.

Reviewed-by: Tim Hudson <tjh@openssl.org>
Reviewed-by: Matthias St. Pierre <Matthias.St.Pierre@ncp-e.com>
Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/7724)

util/find-doc-nits: allow #undef

Reviewed-by: Tim Hudson <tjh@openssl.org>
Reviewed-by: Matthias St. Pierre <Matthias.St.Pierre@ncp-e.com>
Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/7724)

include/openssl/opensslconf.h.in: allow future deprecation for v4.0

Reviewed-by: Tim Hudson <tjh@openssl.org>
Reviewed-by: Matthias St. Pierre <Matthias.St.Pierre@ncp-e.com>
Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/7724)

Configure: allow building without things deprecated up to and including v3.0

Reviewed-by: Tim Hudson <tjh@openssl.org>
Reviewed-by: Matthias St. Pierre <Matthias.St.Pierre@ncp-e.com>
Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/7724)

Switch to MAJOR.MINOR.PATCH versioning and version 3.0.0-dev

We're strictly use version numbers of the form MAJOR.MINOR.PATCH.
Letter releases are things of days past.

The most central change is that we now express the version number with
three macros, one for each part of the version number:

    OPENSSL_VERSION_MAJOR
    OPENSSL_VERSION_MINOR
    OPENSSL_VERSION_PATCH

We also provide two additional macros to express pre-release and build
metadata information (also specified in semantic versioning):

    OPENSSL_VERSION_PRE_RELEASE
    OPENSSL_VERSION_BUILD_METADATA

To get the library's idea of all those values, we introduce the
following functions:

    unsigned int OPENSSL_version_major(void);
    unsigned int OPENSSL_version_minor(void);
    unsigned int OPENSSL_version_patch(void);
    const char *OPENSSL_version_pre_release(void);
    const char *OPENSSL_version_build_metadata(void);

Additionally, for shared library versioning (which is out of scope in
semantic versioning, but that we still need):

    OPENSSL_SHLIB_VERSION

We also provide a macro that contains the release date.  This is not
part of the version number, but is extra information that we want to
be able to display:

    OPENSSL_RELEASE_DATE

Finally, also provide the following convenience functions:

    const char *OPENSSL_version_text(void);
    const char *OPENSSL_version_text_full(void);

The following macros and functions are deprecated, and while currently
existing for backward compatibility, they are expected to disappear:

    OPENSSL_VERSION_NUMBER
    OPENSSL_VERSION_TEXT
    OPENSSL_VERSION
    OpenSSL_version_num()
    OpenSSL_version()

Also, this function is introduced to replace OpenSSL_version() for all
indexes except for OPENSSL_VERSION:

    OPENSSL_info()

For configuration, the option 'newversion-only' is added to disable all
the macros and functions that are mentioned as deprecated above.

Reviewed-by: Tim Hudson <tjh@openssl.org>
Reviewed-by: Matthias St. Pierre <Matthias.St.Pierre@ncp-e.com>
Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/7724)

Switch future deprecation version from 1.2.0 to 3.0

This is in preparation for a switch to MAJOR.MINOR.PATCH versioning
and calling the next major version 3.0.0.

Reviewed-by: Tim Hudson <tjh@openssl.org>
Reviewed-by: Matthias St. Pierre <Matthias.St.Pierre@ncp-e.com>
Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/7724)

util/mkdef.pl: prepare for DEPRECATEDIN_X

This is in preparation for new versioning scheme, where the
recommendation is to start deprecations at major version boundary.

Reviewed-by: Tim Hudson <tjh@openssl.org>
Reviewed-by: Matthias St. Pierre <Matthias.St.Pierre@ncp-e.com>
Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/7724)

Fix some SSL_export_keying_material() issues

Fix some issues in tls13_hkdf_expand() which impact the above function
for TLSv1.3. In particular test that we can use the maximum label length
in TLSv1.3.

Reviewed-by: Tim Hudson <tjh@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/7755)

Revert "Reduce stack usage in tls13_hkdf_expand"

This reverts commit ec0c5f5693e39c5a013f81e6dd9dfd09ec65162d.

SSL_export_keying_material() may use longer label lengths.

Fixes #7712

Reviewed-by: Tim Hudson <tjh@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/7755)

bn/bn_{div|shift}.c: introduce fixed-top interfaces.

Fixed-top interfaces tolerate zero-padded inputs and facilitate
constant-time-ness. bn_div_fixed_top tolerates zero-padded dividend,
but not divisor. It's argued that divisor's length is public even
when value is secret.

[extended tests]

Reviewed-by: Paul Dale <paul.dale@oracle.com>
Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/7589)

bn/bn_div.c: make conditional addition unconditional

and add template for constant-time bn_div_3_words.

Reviewed-by: Paul Dale <paul.dale@oracle.com>
Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/7589)

Configure: recognize div3w modules and add -DBN_DIV3W.

Reviewed-by: Paul Dale <paul.dale@oracle.com>
Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/7589)

Configurations/10-main.conf: remove MIPS bn_div_3_words.

It's being replaced with constant-time alternative.

Reviewed-by: Paul Dale <paul.dale@oracle.com>
Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/7589)

Ignore an auto-generated documentation file

Reviewed-by: Matthias St. Pierre <Matthias.St.Pierre@ncp-e.com>
(Merged from https://github.com/openssl/openssl/pull/7746)

Add an Ed25519 signature maleability test

Reviewed-by: Paul Dale <paul.dale@oracle.com>
(Merged from https://github.com/openssl/openssl/pull/7697)

Disallow Ed25519 signature maleability

Check that s is less than the order before attempting to verify the
signature as per RFC8032 5.1.7

Fixes #7693

Reviewed-by: Paul Dale <paul.dale@oracle.com>
(Merged from https://github.com/openssl/openssl/pull/7697)

Docs: better deprecation text

Expand the text on deprecation to be more descriptive and to refer
back to openssl_user_macros(7).

Incidently, this required a small change in util/find-doc-nits, to
have it skip over any line that isn't part of a block (i.e. that
hasn't been indented with at least one space.  That makes it skip over
deprecation text.

Reviewed-by: Matthias St. Pierre <Matthias.St.Pierre@ncp-e.com>
(Merged from https://github.com/openssl/openssl/pull/7745)

Docs fixup: some man3 pages had unindented code in SYNOPSIS

Reviewed-by: Matthias St. Pierre <Matthias.St.Pierre@ncp-e.com>
(Merged from https://github.com/openssl/openssl/pull/7744)

util/process_docs.pl: handle multiple source directories for .pod files

From now on, the default is to look in both the source directory and
the build directory.

Reviewed-by: Matthias St. Pierre <Matthias.St.Pierre@ncp-e.com>
(Merged from https://github.com/openssl/openssl/pull/7742)

Doc: add doc/man7/openssl_user_macros.pod.in

This manual is a start to describe macros that users can use to affect
what symbols are exported by the public header files.

Because the macro OPENSSL_API_COMPAT has a default that's affected by
configuration choices, we must make it a generated manual.

Reviewed-by: Matthias St. Pierre <Matthias.St.Pierre@ncp-e.com>
(Merged from https://github.com/openssl/openssl/pull/7742)