[clang] [flang] [llvm] Add IR Profile-Guided Optimization (IR PGO) support to the Flang compiler (PR #136098)

[Tarun Prabhu via cfe-commits]

https://github.com/tarunprabhu requested changes to this pull request.

Thanks for the updating the PR. 

There seems to be a [buildkite failure](https://buildkite.com/llvm-project/github-pull-requests/builds/173137#01967cab-3f69-4ec6-8175-49795d1a2819). These failures are often worth checking because it might indicate that your changes might be incompatible with a different build configuration from yours. 

https://github.com/llvm/llvm-project/pull/136098