wine: allow building with experimental wow64 mode

Allows running 32-bit applications on 64-bit native Wine, with no 32-bit libs on the system.
Works at least well enough to run pkgsCross.mingw32.hello.

pkgs/applications/emulators/wine/packages.nix

···
     platforms = [ "x86_64-linux" ];
     mainProgram = "wine64";
   };
+  wineWow64 = callPackage ./base.nix {
+    pname = "wine-wow64";
+    inherit src version supportFlags patches moltenvk;
+    pkgArches = [ pkgs ];
+    mingwGccs = with pkgsCross; [ mingw32.buildPackages.gcc mingwW64.buildPackages.gcc ];
+    geckos = [ gecko64 ];
+    monos =  [ mono ];
+    configureFlags = [ "--enable-archs=x86_64,i386" ];
+    platforms = [ "x86_64-linux" "x86_64-darwin" ];
+    mainProgram = "wine";
+  };
 }

pkgs/top-level/all-packages.nix

···
   winePackages = recurseIntoAttrs (winePackagesFor (config.wine.build or "wine32"));
   wine64Packages = recurseIntoAttrs (winePackagesFor "wine64");
   wineWowPackages = recurseIntoAttrs (winePackagesFor "wineWow");
+  wineWow64Packages = recurseIntoAttrs (winePackagesFor "wineWow64");
 
   wine = winePackages.full;
   wine64 = wine64Packages.full;