Add Profile-Guided Optimization (PGO) support

[zamazan4ik]

Hi!

Here I want to discuss the idea of adding to FPM explicit support for building applications with Profile-Guided Optimization (PGO). According to many articles and benchmarks, PGO can play a huge role in an application optimization path. However, performing PGO optimization manually via tweaking compiler flags can be error-prone. That's why I think adding such a feature to FPM would be helpful.

Some examples of the current situation in other build systems:

• Cargo: No built-in support but there is awesome cargo-pgo
• Bazel: Supports (command-line reference)
• Meson: Supports (b_pgo in the docs)
• CMake: No support yet (GitLab issue)
• SCons: No support yet (GitHub discussion)
• Buck2: No support yet (GitHub discussion)