[Cmake] Hopefully simple CMake problem

[Dejan Lekic]

Hehe, thanks Andy! :)
I have already found (partially) solution... However i've found that it 
doesn't solve all my problems. In generated library i do not have 
objects from platform/linux per example. If you recall my project 
structure, in /lib/librtk.a i would like to have objects from /src/core 
as well as /src/core/platform/linux ... I'll try to find out how to fix 
this problem by myself, so i don't bother people around for every 
problem i have. :)

Best regards, and thanks again!

Dejan