[llvm] [llvm-profgen] Add pgo accuracy metrics (PR #93975)

[via llvm-commits]

lifengxiang1025 wrote:

Thanks for reviewing! @boomanaiden154 @red1bluelost @mtrofin @rlavaee  I have posted one RFC https://discourse.llvm.org/t/rfc-print-pgo-accuracy-metrics/79384.

https://github.com/llvm/llvm-project/pull/93975