[llvm] [InstCombine] optimize powi(X,Y)/X with Ofast (PR #67236)

[Yingwei Zheng via llvm-commits]

https://github.com/dtcxzyw approved this pull request.

LGTM. Waiting for additional approval from @nikic or @jcranmer-intel.

https://github.com/llvm/llvm-project/pull/67236