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

[Tarun Prabhu via cfe-commits]

tarunprabhu wrote:

There is a similar build failure [here](https://github.com/llvm/llvm-project/pull/143603) that seems to be even older. I don't think these are related.

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