[llvm] [LoopUnroll] Use branch probability in multi-exit loop unrolling (PR #164799)

[Marek Sedláček via llvm-commits]

mark-sed wrote:

I'll tag for review "the usuals" for loop-unrolling/rotation stuff @fhahn @nikic @annamthomas 

https://github.com/llvm/llvm-project/pull/164799