build: do not redefine _FORTIFY_SOURCE

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

diff --git a/configure.ac b/configure.ac
index e5e05be..6504144 100644 (file)
--- a/configure.ac
+++ b/configure.ac
@@ -170,7 +170,7 @@ if test "$gl_gcc_warnings" = yes; then
   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
   ])