[llvm] [RISCV][GlobalISel] Legalize G_ADD, G_SUB, G_AND, G_OR, G_XOR on RISC-V Vector Extension (PR #71400)

[Michael Maitland via llvm-commits]

michaelmaitland wrote:

> What's your insight into this behavior and what's your opinion on implementation @michaelmaitland @topperc ? I mean using them in-place works, but it's clumsy.

I experienced this too when I was playing around. Maybe we should do the in place definition, and a future patch can allow `legalIf`, `legalFor` , etc to be overloaded with something like T[].

https://github.com/llvm/llvm-project/pull/71400