Add setFunctionArgs lib function.

Among other things, this will allow *2nix tools to output plain data
while still being composable with the traditional
callPackage/.override interfaces.

nixos/modules/profiles/clone-config.nix

@@ -17,7 +17,7 @@ let
   # you should use files).
   moduleFiles =
     # FIXME: use typeOf (Nix 1.6.1).
-    filter (x: !isAttrs x && !builtins.isFunction x) modules;
+    filter (x: !isAttrs x && !lib.isFunction x) modules;
 
   # Partition module files because between NixOS and non-NixOS files.  NixOS
   # files may change if the repository is updated.