winePackages: enable mingwSupport in base build

With mingwSupport enabled, Wine uses MinGW builds of GCC (compiled for
the i686-w64-mingw32 & x86_64-w64-mingw32 targets) to cross compile
system DLLs as PE executables.

This is used to workaround some basic anticheat software. (See NixOS#103102)

Fedora & Arch Linux also have this enabled by default in their Wine builds:
- Fedora: https://src.fedoraproject.org/rpms/wine/blob/8e216ca407b6c0f78f65f36c5b068c6452701e55/f/wine.spec#_116
- Arch Linux: https://github.com/archlinux/svntogit-community/blob/2435e762eacd989c588200d7cf57d8f4fb2e0cf3/trunk/PKGBUILD#L44

pkgs/top-level/wine-packages.nix

@@ -27,6 +27,7 @@ rec {
     xineramaSupport = true;
     xmlSupport = true;
     sdlSupport = true;
+    mingwSupport = true;
   };
 
   full = base.override {