Determining if the Q_WS_MAC exist failed with the following output:
/usr/bin/make -f CMakeFiles/cmTryCompileExec.dir/build.make CMakeFiles/cmTryCompileExec.dir/build
make[1]: Entering directory `/home/kde-devel/kde/build/KDE/kdelibs/CMakeFiles/CMakeTmp'
/usr/bin/cmake -E cmake_progress_report /home/kde-devel/kde/build/KDE/kdelibs/CMakeFiles/CMakeTmp/CMakeFiles 1
Building C object CMakeFiles/cmTryCompileExec.dir/CheckSymbolExists.o
/usr/bin/gcc  -I/usr/include/qt4   -o CMakeFiles/cmTryCompileExec.dir/CheckSymbolExists.o   -c /home/kde-devel/kde/build/KDE/kdelibs/CMakeFiles/CMakeTmp/CheckSymbolExists.c
/home/kde-devel/kde/build/KDE/kdelibs/CMakeFiles/CMakeTmp/CheckSymbolExists.c: In function ‘main’:
/home/kde-devel/kde/build/KDE/kdelibs/CMakeFiles/CMakeTmp/CheckSymbolExists.c:8: error: ‘Q_WS_MAC’ undeclared (first use in this function)
/home/kde-devel/kde/build/KDE/kdelibs/CMakeFiles/CMakeTmp/CheckSymbolExists.c:8: error: (Each undeclared identifier is reported only once
/home/kde-devel/kde/build/KDE/kdelibs/CMakeFiles/CMakeTmp/CheckSymbolExists.c:8: error: for each function it appears in.)
make[1]: *** [CMakeFiles/cmTryCompileExec.dir/CheckSymbolExists.o] Error 1
make[1]: Leaving directory `/home/kde-devel/kde/build/KDE/kdelibs/CMakeFiles/CMakeTmp'
make: *** [cmTryCompileExec/fast] Error 2