make `-Werror` optional in libatomic/libbacktrace/libgomp/libitm/libsanitizer

* `-Werror` can cause issues when a more recent version of GCC compiles
  an older version:
  - https://bugs.gentoo.org/229059
  - https://bugs.gentoo.org/475350
  - https://bugs.gentoo.org/667104



libatomic/ChangeLog:

	* configure.ac: Support --disable-werror.
	* configure: Regenerate.

libbacktrace/ChangeLog:

	* configure.ac: Support --disable-werror.
	* configure: Regenerate.

libgomp/ChangeLog:

	* configure.ac: Support --disable-werror.
	* configure: Regenerate.

libitm/ChangeLog:

	* configure.ac: Support --disable-werror.
	* configure: Regenerate.

libsanitizer/ChangeLog:

	* configure.ac: Support --disable-werror.
	* aclocal.m4: Include also ../config/warnings.m4.
	* libbacktrace/Makefile.am (WARN_FLAGS): Remove.
	* configure: Regenerate.
	* Makefile.in: Regenerate.
	* asan/Makefile.in: Regenerate.
	* hwasan/Makefile.in: Regenerate.
	* interception/Makefile.in: Regenerate.
	* libbacktrace/Makefile.in: Regenerate.
	* lsan/Makefile.in: Regenerate.
	* sanitizer_common/Makefile.in: Regenerate.
	* tsan/Makefile.in: Regenerate.
	* ubsan/Makefile.in: Regenerate.

Co-Authored-By: Jakub Jelinek <jakub@redhat.com>