The simplest way is to include the sources of your library in your module. If your library doesn't let you do that for license reasons, I guess you should take a look at how SCons handles it (I'm not an expert on this).
You can take model on existing modules to see how things are done. In the case of FreeType, for example, the library was added in the thirdparty folder of Godot (still in source format though).