mingw-w64-pthreads: The C compiler is needed

It was a copy and paste error from the headers derivation. Also test in
release-cross.

pkgs/os-specific/windows/mingw-w64/pthreads.nix

···
-{ stdenvNoCC, callPackage }:
+{ stdenv, callPackage }:
 
 let
   inherit (callPackage ./common.nix {}) name src;
 
-in stdenvNoCC.mkDerivation {
+in stdenv.mkDerivation {
   name = name + "-pthreads";
   inherit src;
 

pkgs/top-level/release-cross.nix

···
     libtool = nativePlatforms;
     libunistring = nativePlatforms;
     windows.wxMSW = nativePlatforms;
+    windows.mingw_w64_pthreads = nativePlatforms;
   };
 
   darwinCommon = {