build: Improve CFLAGS handling.
* configure.ac: Strip any flags matching '-Werror' from CFLAGS before running the tests, and add them back later on.
Previously, the tests were run with empty CFLAGS. This caused
problems, e.g. on Fedora mmap was not detected due to some missing
CFLAGS while running the tests.
- GnuPG-bug-id: T2423
- Fixes-commit: 02eb9fc9d5863abcfed6af704e618f8cac7cc2e8
- Signed-off-by: Justus Winter <justus@g10code.com>