nixos/default.nix: Allow specialArgs to be passed (#442886)

{

  configuration ? import ./lib/from-env.nix "NIXOS_CONFIG" <nixos-config>,

  system ? builtins.currentSystem,

  # This should only be used for special arguments that need to be evaluated when resolving module structure (like in imports).

  # For everything else, there's _module.args.

  specialArgs ? { },

}:

let

  eval = import ./lib/eval-config.nix {

    inherit system;

    inherit system specialArgs;

    modules = [ configuration ];

  };