[CMake] absolute include paths to resource compiler

[jesper at eskilson.se]

Due to some weirdness in Visual Studio, I need to be able to give the
resource compiler an absolute path:

  rc ... -I${CMAKE_SOURCE_DIR}/include

If I put

  include_directories(${CMAKE_SOURCE_DIR}/include)

CMake converts the absolute path to a relative one.


-- 
/Jesper