apple_sdk_11_0: make available for use on x86_64-darwin

doc/stdenv/platform-notes.chapter.md

@@ -60,3 +60,8 @@ Some common issues when packaging software for Darwin:
   ```
 
   The package `xcbuild` can be used to build projects that really depend on Xcode. However, this replacement is not 100% compatible with Xcode and can occasionally cause issues.
+
+- x86_64-darwin uses the 10.12 SDK by default, but some software is not compatible with that version of the SDK. In that case,
+  the 11.0 SDK used by aarch64-darwin is available for use on x86_64-darwin. To use it, reference `apple_sdk_11_0` instead of
+  `apple_sdk` in your derivation and use `pkgs.darwin.apple_sdk_11_0.callPackage` instead of `pkgs.callPackage`. On Linux, this will
+  have the same effect as `pkgs.callPackage`, so you can use `pkgs.darwin.apple_sdk_11_0.callPackage` regardless of platform.

pkgs/os-specific/darwin/apple-sdk-11.0/apple_sdk.nix

@@ -168,8 +168,8 @@ in rec {
   bareFrameworks = (
     lib.mapAttrs framework (import ./frameworks.nix {
       inherit frameworks libs;
-      inherit (pkgs.darwin) libobjc Libsystem;
-      inherit (pkgs.darwin.apple_sdk) libnetwork;
+      inherit (pkgs.darwin.apple_sdk_11_0) libnetwork Libsystem;
+      libobjc = pkgs.darwin.apple_sdk_11_0.objc4;
     })
   ) // (
     lib.mapAttrs privateFramework (import ./private-frameworks.nix {

pkgs/os-specific/darwin/apple-sdk-11.0/default.nix

@@ -1,4 +1,5 @@
-{ stdenvNoCC, fetchurl, newScope, pkgs
+{ stdenvNoCC, fetchurl, newScope, lib, pkgs
+, stdenv, overrideCC
 , xar, cpio, python3, pbzx }:
 
 let
@@ -54,5 +55,35 @@ let
     # questionable aliases
     configd = pkgs.darwin.apple_sdk.frameworks.SystemConfiguration;
     IOKit = pkgs.darwin.apple_sdk.frameworks.IOKit;
+
+    callPackage = newScope (lib.optionalAttrs stdenv.isDarwin rec {
+      inherit (pkgs.darwin.apple_sdk_11_0) stdenv;
+      darwin = pkgs.darwin.overrideScope (_: prev: {
+        inherit (prev.darwin.apple_sdk_11_0) Libsystem LibsystemCross libcharset libunwind objc4 configd IOKit Security;
+        apple_sdk = prev.darwin.apple_sdk_11_0;
+        CF = prev.darwin.apple_sdk_11_0.CoreFoundation;
+      });
+      xcodebuild = pkgs.xcbuild.override {
+        inherit (pkgs.darwin.apple_sdk_11_0.frameworks) CoreServices CoreGraphics ImageIO;
+        inherit stdenv;
+      };
+      xcbuild = xcodebuild;
+    });
+
+    stdenv =
+      let
+        clang = stdenv.cc.override {
+          bintools = stdenv.cc.bintools.override { libc = packages.Libsystem; };
+          libc = packages.Libsystem;
+        };
+      in
+      if stdenv.isAarch64 then stdenv
+      else
+        (overrideCC stdenv clang).override {
+          targetPlatform = stdenv.targetPlatform // {
+            darwinMinVersion = "10.12";
+            darwinSdkVersion = "11.0";
+          };
+        };
   };
 in packages

pkgs/top-level/darwin-packages.nix

@@ -70,7 +70,7 @@ in
 
 impure-cmds // appleSourcePackages // chooseLibs // {
 
-  inherit apple_sdk;
+  inherit apple_sdk apple_sdk_10_12 apple_sdk_11_0;
 
   stdenvNoCF = stdenv.override {
     extraBuildInputs = [];