How do I exclude cpp files being included in project

When I run Generate Visual Studios project files, all files in all subfolders are aggressively included, even supporting files that I don’t with included.

I can see no way of excluding certain subfolders of my project structure from inclusion.
Examples are a library I’m including which includes support for non-ue4 related activities, so I only need include 80% of the files, and omit certain folders.

How do I configure whats included when I Generate Visual Studios Projects?