Disable Windows cross-compilation pending nixpkgs-2511 fix

nixpkgs-2511's crossThreadsStdenv resolves to native Linux stdenv
instead of the cross-compiling stdenv, causing mcfgthread and
mingw_w64_pthreads to fail during GCC cross-compiler bootstrap.
This is a deep nixpkgs issue that can't be fixed via overlays
because cross-compilation package set stages evaluate overlays
independently. Disable Windows builds until upstream is fixed.

Author: angerman

flake.nix

@@ -175,11 +175,9 @@
                   "ghc94"
                   "ghc910"
                  ];
-                 windows-compilers = pkgs:
-                   pkgs.lib.optionalAttrs (__elem system ["x86_64-linux"])
-                   (builtins.removeAttrs (compilers pkgs)
-                     [
-                     ]);
+                 # Windows cross-compilation disabled pending nixpkgs-2511
+                 # crossThreadsStdenv fix (mcfgthread/pthreads bootstrap).
+                 windows-compilers = _pkgs: {};
              in (builtins.mapAttrs (short-name: args:
                   import ./dynamic.nix (args // { withIOG = false; })
                   ) (compilers pkgs)