[clang] [llvm] [WebAssembly] Implement the wide-arithmetic proposal (PR #111598)

[Thomas Lively via cfe-commits]

https://github.com/tlively commented:

Code looks good. I expect you're right about the need to use C++ for codegen, but don't know for sure. @sunfishcode, do you know?

https://github.com/llvm/llvm-project/pull/111598