[llvm] [RISCV] Add combine for shadd family of instructions. (PR #130829)

[Stefan Pintilie via llvm-commits]

stefanp-synopsys wrote:

gentle ping

I believe that I have resolved all of the comments on this issue. I will wait a couple more days for feedback and if I see nothing I will squash and merge. 

https://github.com/llvm/llvm-project/pull/130829