[llvm] [RISCV][VLOPT] Add vsadd and vsaddu to isSupportedInstr (PR #120358)

[Craig Topper via llvm-commits]

topperc wrote:

This can cause a difference in the VXSAT flag, but we make it hard for for software to reliably read that register. So I'm not sure if that should block this or not.

https://github.com/llvm/llvm-project/pull/120358