maintainers/build: enable cross builds

maintainers/scripts/build.nix

@@ -1,10 +1,18 @@
-{ maintainer }:
+{ maintainer
+, localSystem ? { system = args.system or builtins.currentSystem; }
+, system ? localSystem.system
+, crossSystem ? localSystem
+, ...
+}@args:
 
 # based on update.nix
 # nix-build build.nix --argstr maintainer <yourname>
 
+# to build for aarch64-linux using boot.binfmt.emulatedSystems:
+# nix-build build.nix --argstr maintainer <yourname> --argstr system aarch64-linux
+
 let
-  pkgs = import ./../../default.nix {};
+  pkgs = import ./../../default.nix (removeAttrs args [ "maintainer" ]);
   maintainer_ = pkgs.lib.maintainers.${maintainer};
   packagesWith = cond: return: set:
     (pkgs.lib.flatten