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

[Sam Clegg via llvm-commits]

sbc100 wrote:

> Does the rationale in [296ccef](https://github.com/llvm/llvm-project/commit/296ccef70363df9195bc678ad5501dd44de7f8fb) not apply anymore? I guess I can understand why it's unnecessary in case of C symbol + static linking but
> 
> * Is it fine in case of C symbols with dynamic linking?
> * Is it fine in case of JS symbols with static/dynamic linking?
> 
> Now we have only two functions that are labeled with `wasm-import-module`: `invoke`s and `__cxa_matching_catch`s. Are they different from other JS functions?

Yes the `invoke_xxx` and `__cxa_matching_catch_xxx` function are still explicitly marked with import-name and import-module.  

This is because their names are dynamic and we have no way for the static linker to declare their existence in a JS library (at least not without enumerating all of them somehow, which seems hard/impossible). 

One way of thinking about this is that explicitly marking these symbols are imported is something we should avoid, if we can.  But for dynamic symbol names I don't know of any way to avoid it.

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