[CMake] CMake ignores CPLUS_INCLUDE_PATH?

[David Doria]

> You can use $ENV{CPLUS_INCLUDE_PATH} to get the contents of the path.
>

I tried to do this:
INCLUDE_DIRECTORIES(${INCLUDE_DIRECTORIES} $ENV{CPLUS_INCLUDE_PATH})

but it still doesn't find the files (which it DOES find if I specify
the path directly, ie.
INCLUDE_DIRECTORIES(${INCLUDE_DIRECTORIES} /usr/lib/qt-3.3/include/)

and the path is definitely in CPLUS_INCLUDE_PATH:
echo $CPLUS_INCLUDE_PATH
:/home/doriad/src/glui-2.36/src/include/GL:/home/doriad/src/CGAL-3.5/include:/usr/lib/qt-3.3/include/

Thoughts?

Thanks,

David