improve CMP logging according to comments on CMP chunk 7 preview

improve CMP logging according to comments on CMP chunk 7 preview

in particular:
consolidate documentation of CMP logging and error reporting functions
fix compilation problem with clang on some platforms
rename OSSL_CMP_log etc. to ossl_cmp_log etc. since these macros are CMP-internal
move chopping of trailing separator to ossl_cmp_add_error_txt(), also fix handling of leading separator
internalize X509_print_ex_brief() as x509_print_ex_brief()

Reviewed-by: Matt Caswell <matt@openssl.org>
Reviewed-by: Bernd Edlinger <bernd.edlinger@hotmail.de>
(Merged from https://github.com/openssl/openssl/pull/10620)