Fix eval when aliases are disabled

[SuperSandro2000]

       error: attribute 'hostPlatform' missing

       at /nix/store/k7h8k8whqw64rmsg6yhkmmdc82lkczc6-source/flake.nix:66:27:

           65|               # linuxArch is wrong here, it will yield arm64 instead of aarch64.
           66|               config = "${pkgs.hostPlatform.qemuArch}-windows";
             |                           ^
           67|               rustc.config = "${pkgs.hostPlatform.qemuArch}-unknown-uefi";
       Did you mean rustPlatform?

[nikstur]

Thank you!