Evaluate Profile-Guided Optimization (PGO)

[zamazan4ik]

Hi!

Recently I checked Profile-Guided Optimization (PGO) improvements on multiple projects. The results are here. LLVM-related results are here.

Since PGO showed measurable improvements in compiler-like loads (Clang, Clangd, clang-format, GCC, Rustc, etc.) I think it could be useful to check PGO on Cling as well.

We need to perform PGO benchmarks on Cling. And if it shows improvements - add a note about possible improvements Cling performance with PGO. Providing an easier way (e.g. a build option) to build scripts with PGO can be useful for the end-users too.

[p4vook]

I think this is certainly a reasonable way to improve Cling's performance.

[ferdymercury]

Referred to root-project/root#15778