[llvm] [clang] [PGO] Add ability to mark cold functions as optsize/minsize/optnone (PR #69030)

[Matthias Braun via llvm-commits]

MatzeB wrote:

How does this relate to the existing `shouldOptimizeForSize(Function&)` and similar APIs which appear to provide similar functionality at a first glance. If they are the same, then we should have a plan in place to cleanup and only have one system afterwards, if there are important differences, then I wouldn't mind some comments getting added :)

https://github.com/llvm/llvm-project/pull/69030