cmake: LTO/LTCG interprocedural optimization enabling in VS-MSVC context

[roccoarpa]

Investigate why Link Time Optimization (in Visual Studio context known as Link Time Code Generation /LTCG option) does not work in the current solution.

This issue is for potential VS MSVC-native bitpit developers (if any in the next future) just to speed up the compile time of the library. Continous integration could benefit from it too.

Please change priority to the issue, when something moves on this 2 fronts.