[CMake] Don't export symbols but the one I want

[David Demelier]

Hello,

I'm creating a library that use a lot of internal code (not static 
because it should be visible by other compilation units) so I would like 
to don't export any symbols but only the one I want.

Usually you use __declspec(dllexport) for windows but on unix and gcc 
everything is exported and I don't know any portable way to disable this.

Does CMake can handle this problem and export some symbols without using 
ten thousand of #ifdef #endif in C files?

Cheers,

-- 
David Demelier