[CMake] Including source files multiple times

[Mike Jackson]

I have an issue where some common source code is getting included  
multiple times during cmake. I understand why it is happening. My  
question is how to avoid it. Here is the basic project setups.

CommonCodeProject
PVProjectA
PVProjectB

These are being built as ParaView Extra_External_Modules and I would  
like to be able to include either one or both of them in a ParaView  
Build.

PVProjectA and PVProjectB BOTH need the code from CommonCodeProject.  
I have some cmake files inside of CommonCodeProject that lists out  
the various source files. The problem is both PVProjectA and  
PVProjectB include that same cmake file. I have tried setting some  
cmake variables to flag that the files have already been included but  
I don't think I am setting the variable correctly.

Anyone have some pointers on how to achieve the desired results?

Thanks
-- 
Mike Jackson   Senior Research Engineer
Innovative Management & Technology Services