Evaluate using more optimizations like LTO, PGO and PLO

[zamazan4ik]

Request

I suggest enabling more optimizations for the project that can help with achieving better performance and binary size of the project:

• Link-Time Optimization (LTO). I've searched over the build scripts but I didn't find a place where it's enabled (maybe I am wrong). This optimization is supported by all major C++ compilers and can be enabled even via a CMake flags
• Profile-Guided Optimization (PGO). According to my multiple tests, this optimization is specifically useful for various parsing routines, etc. It definitely is worth giving it a try and measuring performance gains from PGO for clp. PGO is also supported by all major C++ compilers like GCC, Clang, MSVC
• Post-Link Optimization (PLO) via tools like LLVM BOLT. This optimization can help to optimize clp better even after applying PGO.

Possible implementation

I think LTO can be quite easily enabled on the CMake level.

Regarding PGO at first, I recommend performing some kind of benchmarking with it on different real-world scenarios. And only if it shows improvement - integrate it in some way into the project. E.g. it also can be done via an option in the build scripts.

PLO I recommend enabling only after PGO since PGO has much fewer possible limitations compared to PLO.