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

[Luke Lau via llvm-commits]

lukel97 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 b0e05a5f04d3225b8ff1319064c88d0249e683d2, let me know if that fixes things.

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