darwin: add mkStub for deprecating frameworks

pkgs/os-specific/darwin/apple-sdk/mk-stub.nix

@@ -0,0 +1,14 @@
+{ stdenvNoCC }:
+
+version: pname:
+stdenvNoCC.mkDerivation {
+  inherit pname version;
+
+  buildCommand = ''
+    mkdir -p "$out"
+    echo "Individual frameworks have been deprecated. See the stdenv documentation for how to use `apple-sdk`" \
+        > "$out/README"
+  '';
+
+  passthru.isDarwinCompatStub = true;
+}

pkgs/top-level/darwin-packages.nix

@@ -32,6 +32,8 @@ let
           pkg
       ) (old.extraBuildInputs or [ ]);
     });
+
+  mkStub = pkgs.callPackage ../os-specific/darwin/apple-sdk/mk-stub.nix { };
 in
 
 makeScopeWithSplicing' {