darwin: replace framework chooser with stubs

  }.${stdenv.hostPlatform.darwinSdkVersion}

  or (throw "Unsupported sdk: ${stdenv.hostPlatform.darwinSdkVersion}");

  # Pick the source of libraries: either Apple's open source releases, or the

  # SDK.

  useAppleSDKLibs = lib.versionAtLeast stdenv.hostPlatform.darwinSdkVersion "11";

  selectAttrs = attrs: names:

    lib.listToAttrs (lib.concatMap (n: lib.optionals (attrs ? "${n}") [(lib.nameValuePair n attrs."${n}")]) names);

  chooseLibs = (

    # There are differences in which libraries are exported. Avoid evaluation

    # errors when a package is not provided.

    selectAttrs (

      if useAppleSDKLibs

        then apple_sdk

        else appleSourcePackages

    ) ["Libsystem" "LibsystemCross" "libcharset" "libunwind" "objc4" "configd" "IOKit"]

  ) // {

    inherit (

      if useAppleSDKLibs

        then apple_sdk.frameworks

        else appleSourcePackages

    ) Security;

  };

  stubs = {

    inherit apple_sdk apple_sdk_10_12 apple_sdk_11_0 apple_sdk_12_3;

  } // lib.genAttrs [

  ] (mkStub apple_sdk.version);

in

impure-cmds // appleSourcePackages // chooseLibs // stubs // {

impure-cmds // appleSourcePackages // stubs // {

  stdenvNoCF = stdenv.override {

    extraBuildInputs = [];