[CMake] Add include files

[Yinon Ehrlich]

Hi,

* I'm new to CMake, trying to convert our existing GNU Makefiles to CMake.
* I have a GCC compilation line that uses GCC's "-include" direction (Instead of having 
multiple identical "#include" lines within the source code.)

  ==> Does anyone has an idea how can I implement this feature with CMake ?
	Maybe I should refrain from using "-include" so to retain the cross-platform ?
	(Actually I can gain the same functionality using the MS's 'stdafx'...)

Thanks in advance,
Yinon