[CMake] Out-of-source build

[Yinon Ehrlich]

Hi,

* I'm new to CMake, trying to convert our existing GNU Makefiles to CMake.
* I need the out-of-source feature, and I want to make sure I do it the 
right way:
    SET(TOPLEVEL "../../..")
    SET(CMAKE_BINARY_DIR ${CMAKE_SOURCE_DIR}/${TOPLEVEL}/bin)
   ... is this the "right" way to do this ?

Thanks in advance,
Yinon