[llvm] [LowerMemIntrinsics] Avoid udiv/urem when type size is a power of 2 (PR #81238)

[Matt Arsenault via llvm-commits]

arsenm wrote:

> Do we need the cl opt testing to force non-pow2 or not?

Doesn't seem worth the hassle 

https://github.com/llvm/llvm-project/pull/81238