[llvm] [SimplifyCFG] Relax `cttz` cost check in `simplifySwitchOfPowersOfTwo` (PR #145159)

[Antonio Frighetto via llvm-commits]

antoniofrighetto wrote:

Added, thanks, shall we take the opportunity extend this to cover reachable default cases too, or better this done separately?

https://github.com/llvm/llvm-project/pull/145159