[CMake] Why are object files built several times?

[Joachim Ziegler]

Hello,

I have two targets that have nearly the same sources:

ADD_EXECUTABLE(startCompletionServer StartCompletionServer.cpp ${BASEFILES})
ADD_EXECUTABLE(test-adler32 test-adler32.cpp ${BASEFILES})

I wonder why every object file belonging to the BASEFILES is built 
twice, once for the first target, once again for the second. This 
doubles my compile time!?

Joachim