[llvm] [SimplifyCFG] Simplify uncond br with icmp & select (PR #165580)

[Kunqiu Chen via llvm-commits]

Camsyn wrote:

The new function `tryToSimplifyUncondBranchWithICmpSelectInIt` is very similar to `tryToSimplifyUncondBranchWithICmpInIt` , deserving a refactorization.

But I have no idea of the best practice to refactor:
1) Merge the two functions into ONE? 
2) Keep the two functions, but extract the common part?

https://github.com/llvm/llvm-project/pull/165580