Silence GCC warnings in CMake C++ standalone project with ROOT classes and dictionaries

[ferhue]

I ended up removing the ROOT dictionary generation, which simplifies greatly the CMakeLists, using ClassDefInline as suggested by @pcanal.

Warning in <MyClass>: The data members of MyClass will not be stored, because it inherits from TObject but does not have its own ClassDef

Well having a LinkDef let you control more carefully what the dictionary does and would give you an opportunity to suppress the warnings. Alternatively you could try a relatively new alternative (so you mileage may vary) and remove the dictionary generation altogether and add a ClassDefInline macro (instead of the ClassDef macro). If it works in you case, it will simply your build while still letting you use forward declaration. Cheers, Philippe.