There's an implementation using setjmp/longjmp in his library here [1]. It uses sigaltstack to assign a newly allocated stack to the coroutine. Marc Lehman's libcoro [2] library does the same.

[1] https://github.com/byuu/higan/blob/master/libco/sjlj.c

[2] http://software.schmorp.de/pkg/libcoro.html