[clang] [llvm] [WebAssembly] Implement an alternative translation for -wasm-enable-sjlj (PR #84137)

[YAMAMOTO Takashi via cfe-commits]

yamt wrote:

@aheejin @sbc100 
let me confirm the plan on this PR.
i can remove the option `-mllvm -experimental-wasm-enable-alt-sjlj` by making it unconditionally true, and update tests, right?


https://github.com/llvm/llvm-project/pull/84137