The C/C++ ecosystem has existed for several decades now and is full of richness. We ported some libraries, but a lot more are out there and waiting to get ported. Actually, many of them, which are listed as follows, work without the need of a full code revamp:
Bullet (http://bulletphysics.org/) is an example of a physics engine that can be ported right away in a few minutes
Irrlicht (http://irrlicht.sourceforge.net/) is one of the many 3D engines that can run on Android
OpenCV (http://opencv.org/) is a computer vision and machine-learning library, which allows your application to "see" and understand the outside world through the camera
GLM (http://glm.g-truc.net/) is a useful library for OpenGL ES 2 to handle matrix calculations in a fully C++ way
Intel Threading Building Block library (https://www.threadingbuildingblocks.org/), or more commonly TBB, is an interesting library for those who need massive parallelization with their native code
Some libraries have been specifically...