* configure.ac (GNULIB_WARN_CFLAGS): Define.
* lib/Makefile.am (AM_CFLAGS): Use $(GNULIB_WARN_CFLAGS)
rather than $(WARN_CFLAGS) and add $(WERROR_CFLAGS).
* gl/lib/regcomp.c.diff: New file.
* gl/lib/regex_internal.c.diff: New file.
* gl/lib/regexec.c.diff: New file.