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

[Heejin Ahn via llvm-commits]

https://github.com/aheejin approved this pull request.

Sorry for the delay.

Chatted with @sbc100 offline, and answering my own question: The reason that we needed this years ago but not anymore is because we generate `libemscripten_js_symbols.so` file that supplies all JS symbol names so wasm-ld knows they should be imported: https://github.com/emscripten-core/emscripten/blob/71e31f4cbbfd922d16fe814769590be4342d1e17/tools/building.py#L126-L136

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