[llvm] [PowerPC] eliminate RLWINM instruction following LBARX as possible (PR #144089)

[Nemanja Ivanovic via llvm-commits]

https://github.com/nemanjai commented:

The description should probably mention that these redundant clear instructions are introduced by `85a9f2e14859b`.

https://github.com/llvm/llvm-project/pull/144089