maint: make it easier to copy FORTIFY_SOURCE snippet

While libvirt intentionally avoids -Wundef (after all, C99
guarantees sane semantics of treating undefined macros as 0),
the glibc insanity of #warning on _FORTIFY_SOURCE coupled with
what some people feel is the black magic of autoconf means
that other projects are likely to copy our snippet verbatim.
We can be nicer to other projects by making it easier to
integrate into projects that use -Wundef.

Suggested by Christophe Fergeau.

* m4/virt-compile-warnings.m4 (LIBVIRT_COMPILE_WARNINGS): Be nice
to other projects using -Wundef.

diff --git a/m4/virt-compile-warnings.m4 b/m4/virt-compile-warnings.m4
index a91d69f46379cfbeb10d35cabfde9a19ef08fcc7..18170474d791d8cf73846214bacfa0c1a8c744cb 100644 (file)
--- a/m4/virt-compile-warnings.m4
+++ b/m4/virt-compile-warnings.m4
@@ -103,8 +103,9 @@ AC_DEFUN([LIBVIRT_COMPILE_WARNINGS],[
     AC_DEFINE([lint], [1],
       [Define to 1 if the compiler is checking for lint.])
     AH_VERBATIM([FORTIFY_SOURCE],
-    [/* Enable compile-time and run-time bounds-checking, and some warnings. */
-     #if __OPTIMIZE__
+    [/* Enable compile-time and run-time bounds-checking, and some warnings,
+        without upsetting newer glibc. */
+     #if defined __OPTIMIZE__ && __OPTIMIZE__
      # define _FORTIFY_SOURCE 2
      #endif
     ])