Add advice on setting CXX at the same time as CC

Reviewed-by: Paul Dale <paul.dale@oracle.com>
(Merged from https://github.com/openssl/openssl/pull/8370)

(cherry picked from commit 284d19c2ced0264bd46de61718aa4a60efa8d175)

diff --git a/INSTALL b/INSTALL
index 7dd051c5115345dc48b7292f1d90149b215bf6a4..0b6a3fd1ec399a62838f63defdd384d26037a395 100644 (file)
--- a/INSTALL
+++ b/INSTALL
@@ -287,6 +287,19 @@
                    Typically OpenSSL will automatically load a system config
                    file which configures default ssl options.
 
+  enable-buildtest-c++
+                   While testing, generate C++ buildtest files that
+                   simply check that the public OpenSSL header files
+                   are usable standalone with C++.
+
+                   Enabling this option demands extra care.  For any
+                   compiler flag given directly as configuration
+                   option, you must ensure that it's valid for both
+                   the C and the C++ compiler.  If not, the C++ build
+                   test will most likely break.  As an alternative,
+                   you can use the language specific variables, CFLAGS
+                   and CXXFLAGS.
+
   no-capieng
                    Don't build the CAPI engine. This option will be forced if
                    on a platform that does not support CAPI.
@@ -662,6 +675,11 @@
                         CC=gcc CROSS_COMPILE=x86_64-w64-mingw32- \
                         ./config -DCOOKIE
 
+                   If CC is set, it is advisable to also set CXX to ensure
+                   both C and C++ compilers are in the same "family".  This
+                   becomes relevant with 'enable-external-tests' and
+                   'enable-buildtest-c++'.
+
   reconf
   reconfigure
                    Reconfigure from earlier data.  This fetches the previous