Stop renaming longjmp in wasm-emscripten-finalize

[kripken]

Instead of finalize renaming emscripten_longjmp_jmpbuf to emscripten_longjmp,
do nothing in finalize. But in the optional --post-emscripten pass, rename it there if
both exist, so that we don't end up using two imports (other optimization passes
can then remove an unneeded import).

Depends on emscripten-core/emscripten#12157 to land first.

[sbc100]

Great!

[aheejin]

This is the reason we generate two different names in LLVM. This is basically the same issue with #3081, meaning in an LLVM IR pass, we don't have wasm final types yet. This change LGTM, and I think we can merge these two names in a separate LLVM backend pass that we planned to make in #3081.

[sbc100]

This is the reason we generate two different names in LLVM.

If there was some way would we could merge these symbols in LLVM at some layer that would be great but it sounds like its just not possible? I guess its OK to continue to maintain them both in emscripten as aliases of each other.

[aheejin]

No it is possible in LLVM, and that's what we decided in #3081. The reason for this and all __invoke renaming was because WebAssemblyLowerEmscriptenEHSjLj is an IR-level pass, which is before isel; if we make a separate MIR level pass that occurs after isel it can resolve all these in LLVM. I first did all these in Binaryen in 2016 or something (when I was an intern ;) ) just because that looked simpler and didn't need a new pass.