[clang] [flang] [llvm] [flang][cmake][perf-training] Optimize flang with PGO and BOLT (PR #198863)

[Amir Ayupov via cfe-commits]

aaupov wrote:

> @aaupov apparently, I need your approval too, can I ask you to look into it?

Can you please move out BOLT change into a separate PR? 

https://github.com/llvm/llvm-project/pull/198863