I am no engineer, but heat build up, and plasma around the body from that speed would seem to make any sensors or radio transmission or reception (gps) an issue. And guidance, whether radar, IR, or optical, would have to have sensors penetrating the insulation and surviving that heat.
Hand it to the Russians. If it is true that all we have done with the wave rider is to go fast, and they do have a functional weapon, this would be a problem...
Guidance can easily be done by a ring laser gyroscope. No external input during flight required.
If I were doing it, I would have a handoff from the navigation system of the launching vehicle immediately prior to launch. After that it is all inertial guidance. Probably good enough.