[llvm] [SimplifyCFG] Do not run `simplifySwitchOfPowersOfTwo` in early invocations (PR #145477)

[Antonio Frighetto via llvm-commits]

antoniofrighetto wrote:

Added, thanks (not exactly testing the original regression, but still managed to show an improvement w/ ConvertSwitchToLookupTable on).

https://github.com/llvm/llvm-project/pull/145477