Besides CFFI there's also cl-autowrap and claw. I haven't used claw myself, but I know cl-autowrap makes wrapping C libraries really easy. It took me about 4 hours and <200 lines of code to have a complete, usable binding for GDAL, and most of that was in convenience functions.

I'm curious to see what happens with the C++ support in claw. They're working on it, but I'm skeptical. I haven't had much luck using arbitrary C++ libraries from any language other than C++.

And I don't know what the author means by "somewhat rarer" in this context, but I personally use C libraries from CL all the time. Almost every CL project I work on, now that I think about it.