[clang] [llvm] [PowerPC] Fix behavior of rldimi/rlwimi/rlwnm builtins (PR #85040)

[Chen Zheng via cfe-commits]

https://github.com/chenzheng1030 commented:

Looks almost good to me though I have a comment for the all one mask case.

https://github.com/llvm/llvm-project/pull/85040