I have same experience with you, when I tried to deal with a c++ library that was co-developed with the main project. In lieu of an ubiquitous package manager

I have same experience with you, when I tried to deal with a c++ library that was co-developed with the main project. In lieu of an ubiquitous package manager / module support what other options are there for c++? Keep a text file in the main project with the version of the library you need to compile it ?