[CMake] CMake won't clean generated files for Xcode

[Tron Thomas]

I am trying to configure a project with CMake that uses the CxxTest 
testing framework.  CxxTest will generate source files that may be added 
into application that test the software.  A macro has been written that 
will create custom commands for generated the needed source file.

However, when I used CMake to create a Xcode project on Mac OS X, the 
clean process will not delete the files generated by CxxTest.  This is 
true even when using the SET_DIRECTORY_PROPERTIES command with the 
ADDITIONAL_MAKE_CLEAN_FILES.  What can be done so the Xcode will delete 
these files when necessary?