webrtc-sys: macOS link fails with framework 'Appkit' not found

[BegoniaHe]

Summary

webrtc-sys/build.rs links framework=Appkit on macOS. The real framework name is AppKit (capital K). Newer Apple ld treats framework names as case-sensitive, so linking a crate that depends on webrtc-sys fails with:

ld: framework 'Appkit' not found
clang: error: linker command failed with exit code 1

The misspelling is still on main and in published crates (0.3.28 through 0.3.43). Older linkers ignored the case, so this did not show up until a newer Xcode/ld.

Fix

webrtc-sys/build.rs (macos branch):

-            println!("cargo:rustc-link-lib=framework=Appkit");
+            println!("cargo:rustc-link-lib=framework=AppKit");

That is the only Appkit occurrence in the crate.

Environment

• OS: macOS 15.7.9 (arm64)
• Xcode: 26.3 (build 17C529)
• rustc: 1.95.0
• webrtc-sys: 0.3.28 (also present on main / 0.3.43)

Reproduction

Link any macOS binary that depends on webrtc-sys with a current Xcode toolchain. The linker command includes -framework Appkit and fails as above.

Happy to open a PR with the one-line change if that's preferred.