[libcxx] [libcxxabi] [libunwind] [llvm] [libc++][WIP] Move the libc++ test format to Lit (PR #90803)

[Mark de Wever via cfe-commits]

https://github.com/mordante commented:

I like the idea of this patch.

I mainly glossed over the patch to see what it does since it's WIP. Some comments.

https://github.com/llvm/llvm-project/pull/90803