[llvm] [clang] [WebAssembly] Mark externref as not being valid vector elements (PR #71069)

[Nikita Popov via cfe-commits]

nikic wrote:

@pmatos If you don't want to go all the way to target extension types, is it possible to gracefully handle this in wasm's TTI cost model? Return an invalid or very high cost in this case?

https://github.com/llvm/llvm-project/pull/71069