[clang] [flang] [llvm] Fix and reapply IR PGO support for Flang (PR #142892)

[Tarun Prabhu via llvm-commits]

https://github.com/tarunprabhu approved this pull request.

Thanks. I'll merge this tomorrow morning (my time), so I can keep an eye on the buildbots, just in case.

https://github.com/llvm/llvm-project/pull/142892