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/giflib/4.1.nix

@@ -8,7 +8,7 @@ stdenv.mkDerivation {
     sha256 = "1v9b7ywz7qg8hli0s9vv1b8q9xxb2xvqq2mg1zpr73xwqpcwxhg1";
   };
 
-  hardening_format = false;
+  hardeningDisable = [ "format" ];
 
   meta = {
     branch = "4.1";

pkgs/development/libraries/giflib/libungif.nix

@@ -7,6 +7,6 @@ stdenv.mkDerivation {
     md5 = "efdfcf8e32e35740288a8c5625a70ccb";
   };
 
-  hardening_format = false;
+  hardeningDisable = [ "format" ];
 }