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

[Tarun Prabhu via cfe-commits]

tarunprabhu wrote:

@fanju110 

The PR caused some buildbot failures, so I have [reverted](https://github.com/llvm/llvm-project/commit/597340b5b666bdee2887f56c111407b6737cbf34) it. You can see the error [here](https://lab.llvm.org/buildbot/#/builders/203/builds/12089/steps/7/logs/stdio). 

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