build: Avoid warnings about _FORTIFY_SOURCE

Gentoo (and others) define _FORTIFY_SOURCE=2 by default.  We redefine
it, resulting in an error / configure failure.

diff --git a/acinclude.m4 b/acinclude.m4
index ac29c2b..13fd52c 100644 (file)
--- a/acinclude.m4
+++ b/acinclude.m4
@@ -12,7 +12,7 @@ AC_DEFUN([AC_PROG_CC_PIE], [
 
 AC_DEFUN([COMPILER_FLAGS], [
        if (test "${CFLAGS}" = ""); then
-               CFLAGS="-Wall -O2 -D_FORTIFY_SOURCE=2"
+               CFLAGS="-Wall -O2 -U_FORTIFY_SOURCE -D_FORTIFY_SOURCE=2"
        fi
        if (test "$USE_MAINTAINER_MODE" = "yes"); then
                CFLAGS="$CFLAGS -Werror -Wextra"