zlib/cross: Fix build for Darwin.

Provide the correct cross ranlib, because native ranlib will fail.

Signed-off-by: aszlig <aszlig@redmoonstudios.org>

pkgs/development/libraries/zlib/default.nix

@@ -36,6 +36,8 @@ stdenv.mkDerivation rec {
       "-f" "win32/Makefile.gcc"
       "PREFIX=${stdenv.cross.config}-"
     ] ++ (if static then [] else [ "SHARED_MODE=1" ]);
+  } // stdenv.lib.optionalAttrs (stdenv.cross.libc == "libSystem") {
+    makeFlags = [ "RANLIB=${stdenv.cross.config}-ranlib" ];
   };
 
   # zlib doesn't like the automatic --disable-shared from the Cygwin stdenv.