Restore check for container not defining `nixpkgs.hostPlatform` option

                      extraConfig = { options, ... }: {

                        _file = "module at ${__curPos.file}:${toString __curPos.line}";

                        config = {

                          nixpkgs = { inherit (host.pkgs.stdenv) hostPlatform; };

                          nixpkgs =

                            if options.nixpkgs?hostPlatform

                            then { inherit (host.pkgs.stdenv) hostPlatform; }

                            else { localSystem = host.pkgs.stdenv.hostPlatform; }

                          ;

                          boot.isContainer = true;

                          networking.hostName = mkDefault name;

                          networking.useDHCP = false;