[libcxxabi] [libunwind] [llvm] fix Wasm exceptions + coop threading + shared libraries (PR #222747)

[Heejin Ahn via cfe-commits]

https://github.com/aheejin commented:

Mostly LGTM % nits. Also I think doing this unconditionally is fine because it doesn't seem to increase code size and the performance impact will be negligible given that this only runs on `catch` clauses (not on destructors with `catch_all`s).

This has to land after https://github.com/emscripten-core/emscripten/pull/27753 to pass Emscripten autorollers.

https://github.com/llvm/llvm-project/pull/222747