[llvm] [RISCV] Add IsSignExtendingOpW to AMO*_W instructions. (PR #72349)

[Yingwei Zheng via llvm-commits]

dtcxzyw wrote:

> > I think it also holds for `lr.w` and `amocas.w`.
> 
> Do lr.w instructions exist at that point in the pipeline?

`lr.w` is generated during the atomic pseudo instruction expansion. Sorry for my mistake.

https://github.com/llvm/llvm-project/pull/72349