luajitPackages.mpack.meta.broken = true

It seems only to link succesfully to vanilla lua.
http://hydra.nixos.org/build/49554613

pkgs/top-level/lua-packages.nix

@@ -461,6 +461,8 @@ let
       homepage = "https://github.com/tarruda/libmpack";
       platforms = stdenv.lib.platforms.linux;
       license = stdenv.lib.licenses.mit;
+      # gcc -llua fails with luajit
+      broken = (builtins.parseDrvName lua.name).name != "lua";
     };
   };