[llvm] Introduce UnpredictableProfileLoader for PMU branch-miss profiles (PR #99027)

[Sotiris Apostolakis via llvm-commits]

sapostolakis wrote:

> @sapostolakis does CMOV optimization take advantage of the hint?

Yes, it checks the !unpredictable metadata (https://github.com/llvm/llvm-project/blob/main/llvm/lib/CodeGen/SelectOptimize.cpp#L917). So, given that this PR adds  !unpredictable metadata, it would work for the select-optimize pass.

https://github.com/llvm/llvm-project/pull/99027