[PATCH] RFC: PR78905 define _GLIBCXX_RELEASE macro

[Jonathan Wakely <jwakely at redhat dot com>]

As I said in https://gcc.gnu.org/ml/libstdc++/2017-01/msg00109.html
the __GLIBCXX__ macro is useless, but is the closest thing we have to
a version macro for libstdc++. This matters when using libstdc++ with
Clang or Intel icc or other compilers, because you can't check the
__GNUC__ macro. I've seen several requests for a way to check the
libstdc++ version, or complaints that there is no way to do it.

This patch adds a new _GLIBCXX_RELEASE macro that contains the same
value as __GNUC__ i.e. the major release number.

- Yes, it only contains the major number. We could in theory have
 _GLIBCXX_MAJOR and _GLIBCXX_MINOR instead, but between
 _GLIBCXX_RELEASE and __GLIBCXX__ you can identify the release branch
 and a date within that branch.

- The name is "RELEASE" because we used to define _GLIBCXX_VERSION
 many years ago, but it was a string literal and this is an integer.
 To avoid problems for any old code checking for _GLIBCXX_VERSION I
 chose a different name.

Thoughts?


	PR libstdc++/78905
	* include/Makefile.am (_GLIBCXX_RELEASE): Set value.
	* include/Makefile.in: Regenerate.
	* include/bits/c++config (_GLIBCXX_RELEASE): Add #define.
	* testsuite/ext/profile/mutex_extensions_neg.cc: Use lineno of 0 in
	dg-error.

Attachment: patch.txt
Description: Text document