* configure.ac (_FORTIFY_SOURCE): Define only when optimizing.

This ports to glibc 2.15 or later, when configured with
--enable-gcc-warnings.  See Eric Blake in
<http://lists.gnu.org/archive/html/bug-grep/2012-09/msg00000.html>.

ChangeLog

+2012-09-01  Paul Eggert  <eggert@cs.ucla.edu>
+
+	* configure.ac (_FORTIFY_SOURCE): Define only when optimizing.
+	This ports to glibc 2.15 or later, when configured with
+	--enable-gcc-warnings.  See Eric Blake in
+	<http://lists.gnu.org/archive/html/bug-grep/2012-09/msg00000.html>.
+
 2012-09-01  Daniel Colascione  <dan.colascione@gmail.com>
 
 	* configure.ac: Introduce term_header variable, which holds the

configure.ac

@@ -737,8 +737,13 @@ else
   gl_WARN_ADD([-funit-at-a-time])
 
   AC_DEFINE([lint], [1], [Define to 1 if the compiler is checking for lint.])
-  AC_DEFINE([_FORTIFY_SOURCE], [2],
-    [enable compile-time and run-time bounds-checking, and some warnings])
+  AH_VERBATIM([FORTIFY_SOURCE],
+  [/* Enable compile-time and run-time bounds-checking, and some warnings,
+      without upsetting glibc 2.15+. */
+   #if defined __OPTIMIZE__ && __OPTIMIZE__
+   # define _FORTIFY_SOURCE 2
+   #endif
+  ])
   AC_DEFINE([GNULIB_PORTCHECK], [1], [enable some gnulib portability checks])
 
   # We use a slightly smaller set of warning options for lib/.