How to handle a c++ project configuration?

We have a c++ code stack, that we need to share across two different projects, need to specialise at compile time for either of the projects.

The stack has a set of core functionality which will be common across two projects. For project specific code, we can think of 1. Set of features which have common implementation but optional between projects 2. Some features might have different implementation across the projects

Either case, core functionality should be able to plugin the project specific code.

We are thinking of having libraries for point 1, and macros for point 2. Is there any cleaner precedent or constructs that we could follow in this case?