[CMake] absolute include paths to resource compiler

[Jesper Eskilson]

>> 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.
>> 
>> 
>What is the weirdness?   It should work without a full path?

Building works, but the resource view in Visual Studio can for some
reason not locate the resource file (in
${CMAKE_SOURCE_DIR}/include). It seems as if Visual Studio does not
always expand relative paths the same way. The result is that we can't
edit our resource files in Visual Studio, since Visual Studio can't
find them.

-- 
/Jesper