Yeah, clang does not provide pkgconfig files.
https://bugs.llvm.org/show_bug.cgi?id=9405
There are some other places it looks at:
https://crates.io/crates/clang-sys/0.8.0
You end up needing to set LIBCLANG_PATH no matter what here. It also looks for llvm-config, but we don’t put libclang there. So LIBCLANG_PATH is pretty much required. We could make this easier with a setup hook though.