[llvm] [RISCV] Re-work how VWADD_W_VL and similar _W_VL nodes are handled in combineOp_VLToVWOp_VL. (PR #159205)

[Craig Topper via llvm-commits]

topperc wrote:

> LGTM.
> 
> I think this needs to be backported to llvm 21?

I think llvm 21 needs a fix, but I think I want this fix to be tested for a bit.

https://github.com/llvm/llvm-project/pull/159205