When _FORTIFY_SOURCE is defined by the compiler or via flags, as
it is on Gentoo, do not override it. Otherwise we get many
redefinition warnings.
* configure.ac (FORTIFY_SOURCE): Check if _FORTIFY_SOURCE is defined.
This addresses http://bugs.gnu.org/12714
AH_VERBATIM([FORTIFY_SOURCE],
[/* Enable compile-time and run-time bounds-checking, and some warnings,
without upsetting glibc 2.15+. */
- #if defined __OPTIMIZE__ && __OPTIMIZE__
+ #if !defined _FORTIFY_SOURCE && defined __OPTIMIZE__ && __OPTIMIZE__
# define _FORTIFY_SOURCE 2
#endif
])