[llvm] [WebAssembly] Add getMinVectorRegisterBitWidth overriding (PR #189465)

[Sam Parker via llvm-commits]

sparker-arm wrote:

Also, the wasm-perf 'microkernels' are there for two functions: to test correctness and compare how the vectorizer does against scalar code. Please feel free to add kernels for the SLP vectorizer, as I've only added ones for the loop vectorizer so far. 

https://github.com/llvm/llvm-project/pull/189465