bug#15663: _FORTIFY_SOURCE compilation error: Redefinition with GCC 4.7.3 under Gentoo

[Paul Eggert]

behoffski wrote:
> I can suggest two ways of dealing with this: Either respect any previous 
> definition:

That's what Emacs does, so I changed 'grep' to do that, as follows.
Thanks for reporting the bug.

>From 15e16023b8318b6eece1325eb2ea9d3fcfbc77ad Mon Sep 17 00:00:00 2001
From: Paul Eggert <address@hidden>
Date: Sun, 20 Oct 2013 15:05:14 -0700
Subject: [PATCH] build: port to platforms that predefine _FORTIFY_SOURCE

Problem reported by Brenton Hoff (Bug#15663).
* configure.ac (_FORTIFY_SOURCE): Don't define if already defined.
This is what Emacs does.
---
 configure.ac | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/configure.ac b/configure.ac
index 5c93d04..6ce7237 100644
--- a/configure.ac
+++ b/configure.ac
@@ -159,7 +159,7 @@ 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
   ])
-- 
1.8.3.1