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.

pkgs/development/beam-modules/lib.nix

@@ -6,8 +6,8 @@ rec {
   */
   callPackageWith = autoArgs: fn: args:
     let
-      f = if builtins.isFunction fn then fn else import fn;
-      auto = builtins.intersectAttrs (builtins.functionArgs f) autoArgs;
+      f = if pkgs.lib.isFunction fn then fn else import fn;
+      auto = builtins.intersectAttrs (stdenv.lib.functionArgs f) autoArgs;
     in f (auto // args);
 
   callPackage = callPackageWith pkgs;