Russ implemented his own setmcontext and getmcontext functions to work on systems that doesn't properly support ucontext. So I don't think you really need ucontext support in your libc.
By the way, I maintain an updated version of libtask: https://github.com/0intro/libtask I've used it on quite a few places over the years, but I only on POSIX systems so far. -- David du Colombier
