[CMake] Source In Multiple Directories

[Joe Cotellese]

Hello,

I am trying to build a library which has sources in two directories. The 
structure is as follows

 >prj
 >----common
 >----prjsrc

I'm creating a top level CMakeList file in prj. My question is what is 
the best way to structure my CMakeList file. I don't want to create 
libraries for both common and prjsrc. I'd rather just reference the 
source in the parent CMakeList file. Is this legal and does it make 
sense? Is there a better way to reference code in multiple directories?

Thanks,
Joe Cotellese