[clang] [libcxxabi] [llvm] Add support for WASI builds (PR #91051)

[Luca Versari via cfe-commits]

veluca93 wrote:

Ping

(I suspect that the assigned reviewers are likely not the most appropriate, but I would be unsure on how to change them and to whom)

https://github.com/llvm/llvm-project/pull/91051