[llvm] [WebAssembly] Implement GlobalISel (PR #157161)

[Demetrius Kanios via llvm-commits]

QuantumSegfault wrote:

I wonder how much #159880 and the already merged #158269 would do to help me remove the custom patterns for p0.

It just feels like I'm missing something simple to say p0 goes in either I32 or I64 depending on HwMode. Doesn't seem like this new stuff addresses that.

https://github.com/llvm/llvm-project/pull/157161