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

[YAMAMOTO Takashi via cfe-commits]

yamt wrote:

> Given that we don't need `setjmpTableSize` anymore and `setjmpTable` doesn't change, we don't need the whole block here from line 1463 ~ line 1503 doing SSA updates anymore:

i get errors like the following if i simply put the SSA update things in `!EnableWasmAltSjLj` block.
i need to investigate.
```
spacetanuki% /Volumes/PortableSSD/llvm/build/bin/clang --sysroot /opt/wasi-sdk-21.0/share/wasi-sysroot -resource-dir /Volumes/PortableSSD/llvm/llvm/lib/clang/17 --target=wasm32-wasi -Os -c -mllvm -wasm-enable-sjlj -mllvm -experimental-wasm-enable-alt-sjlj a.c  
Instruction does not dominate all uses!
  %val = load i32, ptr %val_gep, align 4
  %setjmp.ret = phi i32 [ 0, %entry.split ], [ %val, %setjmp.dispatch ]
in function f
fatal error: error in backend: Broken function found, compilation aborted!
PLEASE submit a bug report to https://github.com/llvm/llvm-project/issues/ and include the crash backtrace, preprocessed source, and associated run script.
Stack dump:
0.      Program arguments: /Volumes/PortableSSD/llvm/build/bin/clang --sysroot /opt/wasi-sdk-21.0/share/wasi-sysroot -resource-dir /Volumes/PortableSSD/llvm/llvm/lib/clang/17 --target=wasm32-wasi -Os -c -mllvm -wasm-enable-sjlj -mllvm -experimental-wasm-enable-alt-sjlj a.c
1.      <eof> parser at end of file
2.      Code generation
3.      Running pass 'Function Pass Manager' on module 'a.c'.
4.      Running pass 'Module Verifier' on function '@f'
```

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