[llvm] [PGO] Supporting code for always instrumenting loop entries (PR #116789)

[Christian Ulmann via llvm-commits]

https://github.com/Dinistro commented:

Dropped a bunch of nit comments. The general idea makes sense to me and I think we can soonish open this for general reviews of people experienced with these components.

https://github.com/llvm/llvm-project/pull/116789