如何使用多个相互依赖的子目录构建一个c++项目?

I have a C++ project where I've used directories as more of an organizational element -- the way one might use packages in Java or directories in PHP. Directories are not intended to be self-sufficient elements, but rather just a way of organizing the whole of the project and keeping me from being overwhelmed by sources. How can I construct my CMakeLists.txt files to deal with this? Making the directories libraries doesn't seem to fit here, since they are all interdependent and not intended to be used that way.I have a C++ project where I've used directorie