Auto merge of servo#28978 - yvt:patch/nix-darwin-framework, r=jdm

`etc/shell.nix`: Add `AppKit` to `buildInputs` on Darwin

System framework dependencies need to be specified explicitly on Darwin.

Fixes a linker error when building Servo inside a Nix shell on macOS.

Signed-off-by: yvt <i@yvt.jp>

---
- [x] `./mach build -d` does not report any errors
- [x] `./mach test-tidy` does not report any errors
- [ ] These changes fix #___ (GitHub issue number if applicable)

---
- [ ] There are tests for these changes OR
- [x] These changes do not require tests because they don't affect the production code

Author: bors-servo

etc/shell.nix

@@ -20,7 +20,9 @@ clangStdenv.mkDerivation rec {
     # Build utilities
     cmake dbus gcc git pkgconfig which llvm autoconf213 perl yasm m4
     (python3.withPackages (ps: with ps; [virtualenv pip dbus]))
-  ];
+  ] ++ (lib.optionals stdenv.isDarwin [
+    darwin.apple_sdk.frameworks.AppKit
+  ]);
 
   LIBCLANG_PATH = llvmPackages.clang-unwrapped.lib + "/lib/";