[llvm] [WebAssembly] Mask undef shuffle lanes (PR #149084)

[Sam Parker via llvm-commits]

sparker-arm wrote:

> which VMs have you tested this with?

With ~20 lines of code into V8 to notice the AND mask, this change gave me ~10% speedup on my microbenchmark suite for memory interleaving.

https://github.com/llvm/llvm-project/pull/149084