Earlier quoted context omitted.
Getcontext/setcontext has always allowed for coroutines in C. This just adds a sugar layer of nonblocking functions that allows a runtime layer to switch between contexts (coroutines), just like Go.
The ucontext stuff is nice but why was it deprecated? It's generally not a problem on x86, but in my experience for other platforms, it gets messy quickly. It would be nice if a replacement or a "de-deprecated" was around.
makecontext cannot be correctly represented by the C type system.