As @slf commented any C/C++ code can be compiled for iOS devices. so you can use any of these libraries:
- dlib is a library which has many useful tools including machine learning.
- MicroPather is a path finder and A* solver (astar or a-star) written in platform independent C++ that can be easily integrated into existing code.
- Here is a list of some AI libraries suggested on OGRE3D website. Seems they are mostly written in C++ and at least most of them are not depended on OGRE engine itself.