Use general hardening flag toggle lists

The following parameters are now available:

  * hardeningDisable
    To disable specific hardening flags
  * hardeningEnable
    To enable specific hardening flags

Only the cc-wrapper supports this right now, but these may be reused by
other wrappers, builders or setup hooks.

cc-wrapper supports the following flags:

  * fortify
  * stackprotector
  * pie (disabled by default)
  * pic
  * strictoverflow
  * format
  * relro
  * bindnow

pkgs/development/libraries/mp4v2/default.nix

@@ -17,7 +17,7 @@ stdenv.mkDerivation rec {
   # `faac' expects `mp4.h'.
   postInstall = "ln -s mp4v2/mp4v2.h $out/include/mp4.h";
 
-  hardening_format = false;
+  hardeningDisable = [ "format" ];
 
   meta = {
     homepage = http://code.google.com/p/mp4v2;