Missing `cmake/Modules/GetDarwinLinkerVersion.cmake`

When building on macOS, the CMake call fails because of missing files:

```
2025-11-07T03:39:53.9155440Z  │ │ CMake Error at $SRC_DIR/src/clang/CMakeLists.txt:323 (get_darwin_linker_version):
2025-11-07T03:39:53.9497850Z  │ │   Unknown CMake command "get_darwin_linker_version".
```

Looks like you need to start including the top-level `cmake` directory from LLVM.