With the update to LLVM 15, which was great, CH now has multiple copies of the same LLVM submodules:

• libunwind: Unwind fork. AFAICT heavily modified.
• libcxx: Only minor differences with libc++ (LLVM 14)
• libcxxabi: Only minor differences with libc++-abi (LLVM 14)
• llvm-project: Has all the submodules (LLVM 15)

I think it'd be way easier to keep things in sync and update properly if at least libcxx, libcxxabi were using the llvm-project submodule code instead. I'm not sure about libunwind since that seems to include lots of changes that might be harder to integrate and keep updated.