cmake: add cross compilation support

note that on Windows,

    GET_PROPERTY(METAPOD_BINARYTREEMODEL_EXECUTABLE
                 TARGET metapod_binarytreemodel PROPERTY LOCATION)

Does not return anything useful: the _d prefix used in debug is missing,
there are variables to be expanded.
See http://www.cmake.org/cmake/help/v2.8.10/cmake.html#prop_tgt:LOCATION

Instead of the executable location, we use the target name.

Change-Id: Ice85eef2c0b81a280dd754e6719c448fc471344c