[llvm] [RISCV] Don't commute with shift if it would break sh{1,2,3}add pattern (PR #119527)

[Hans Wennborg via llvm-commits]

zmodem wrote:

> > We're hitting this too (https://crbug.com/388039781). Is there an ETA for landing the fix? If it will take a while, can we revert the breaking change in the meantime?
> 
> In the interest of keeping main green I've gone ahead and cherry-picked the fix ahead of the PR in [b0e05a5](https://github.com/llvm/llvm-project/commit/b0e05a5f04d3225b8ff1319064c88d0249e683d2), let me know if that fixes things.

Confirmed that fixes the case I was hitting locally. Thanks!

https://github.com/llvm/llvm-project/pull/119527