[lld] [llvm] [WebAssembly] Add exnref type (PR #93586)

[Derek Schuff via llvm-commits]

dschuff wrote:

also a general question: will we actually need to use a table of exnrefs to compile C++ exceptions (I think not, right?). I guess that also means we don't need to add support for representing exnrefs in LLVM IR (to go along with the existing funcref/externref support), at least for now.

https://github.com/llvm/llvm-project/pull/93586