Nix / NixOS

Hey guys, I have a project which I want to cross-compile to windows (because I don't want to install windows on my machine, nor do I plan on developing on windows) and eventually MacOS.

All I really need is to know that it will compile for & run on windows.

This is what I tried, but I'm not sure what the best approach is here. Searching online didn't yield any conclusive results either.

{
  description = "cross-compile dev env";

  inputs = {
    nixpkgs.url = "github:NixOS/nixpkgs/nixpkgs-unstable";
  };

  outputs = { nixpkgs, ... }:
    let
      supportedSystems = ["x86_64-linux"];
      eachSystem = fn: nixpkgs.lib.genAttrs supportedSystems (system:
        fn nixpkgs.legacyPackages.${system}
      );
    in
    {
      #1 this is what I tried at first,
      # but it created conflicts in the environment (obviously)
      devShells = eachSystem (pkgs: {
        default = pkgs.mkShell.override { stdenv = pkgs.gcc15.stdenv; } {
          packages = with pkgs; [
            ...
            pkgsCross.mingwW64.buildPackages.gcc15
          ];
        };
      });

      #2 this is probably a better solution?
      devShells = eachSystem (pkgs: let packages = with pkgs; [
        ...
      ]; in {
        default = pkgs.mkShell.override { stdenv = pkgs.gcc15.stdenv; } {
          inherit packages;
        };

        windows = pkgs.pkgsCross.mingwW64.mkShell { 
          inherit packages;
        };
      });
    };
}

The project is just a C program which compiles using a Makefile. I stripped out dependencies etc. from the flake.