Linking against external local C++ libraries gradle can't find

I’m trying to link against libraries like boost_regex and gazebo_transport, and running into problems.
I’m coming from CMake, where I can just use FindPackage, target_link_library, and link_directories to find stuff for me.

Essentially, there are many libraries I want to link against that are installed by the user at /usr/lib/x86_64-linux-gnu. Unfortunately, when I add lib library: gazebo_transport to my build.gradle it complains that

Could not locate library 'gazebo_transport'.
> NativeLibrarySpec with name 'gazebo_transport' not found.
> Project does not have any prebuilt library repositories.

here is my full build.gradle

I found in someone use linkage: 'api' but I’m not sure where that’s documented.

So, how can I link against 3rd party libraries installed on my system? I also need this to work on windows!