[llvm] [WebAssemblyLowerEmscriptenEHSjLj] Avoid setting import_name where possible (PR #128564)

[Sam Clegg via llvm-commits]

sbc100 wrote:

Gentle ping (I've got an emscripten-side change waiting on this).   BTW I ran the whole other and core tests suites in emscripten with this patch applied.

https://github.com/llvm/llvm-project/pull/128564