Gentoo already sets -D_FORTIFY_SOURCE=2 by default in GCC (patched in), so
we need to avoid doing this in packages to avoid redefinition errors if
we try to upgrade to e.g. =3.

So, no effect on users, but important to stop issues w/ F_S=3.
--- a/config-scripts/cups-compiler.m4
+++ b/config-scripts/cups-compiler.m4
@@ -106,8 +106,8 @@ AS_IF([test -n "$GCC"], [
     ], [
 	# Otherwise use the Fortify enhancements to catch any unbounded
 	# string operations...
-	CFLAGS="$CFLAGS -D_FORTIFY_SOURCE=2"
-	CXXFLAGS="$CXXFLAGS -D_FORTIFY_SOURCE=2"
+	CFLAGS="$CFLAGS"
+	CXXFLAGS="$CXXFLAGS"
     ])
 
     # Default optimization options...