Add in-source Tracy profiler

[foxtran]

This patch adds support of Tracy profiler on hot-path of GFN2 method. I did not profile everything, but the most interesting parts are covered. Anyway, there is a room for optimizing and for more profiling. Have fun! 🎉

Only CMake build system is supported.
Tested with GCC and Intel LLVM compiler sets.

[awvwgk]

This seems quite invasive for profiler usage to me.

I guess for the __LINE__ directive there is not really an alternative here, but most other preprocessor usage is abstractable here. I would recommend to make a xtb_tracing or xtb_profiling module which defines a derived type to hold profiler information together with a push / pop (or begin / end) procedure and limit the preprocessor usage to there.

[foxtran]

@awvwgk, what is minimum supported version of GCC? Do you keep some version that must compile xtb always?