gmp{4,5}: mark broken on x86_64-darwin

pkgs/development/libraries/gmp/4.3.2.nix

@@ -69,6 +69,7 @@ let self = stdenv.mkDerivation rec {
 
     maintainers = [ ];
     platforms = stdenv.lib.platforms.all;
+    badPlatforms = [ "x86_64-darwin" ];
   };
 };
   in self

pkgs/development/libraries/gmp/5.1.x.nix

@@ -71,6 +71,7 @@ let self = stdenv.mkDerivation rec {
       '';
 
     platforms = platforms.all;
+    badPlatforms = [ "x86_64-darwin" ];
     maintainers = [ maintainers.peti ];
   };
 };