This thread details the coroutines API for C++: https://gcc.gnu.org/ml/gcc-patches/2020-01/msg01096.html
Just like we map to C++ exceptions, it's probably worthwhile to have coroutines that map cleanly to C++ coroutines so that we can use GCC/Clang/VCC machinery without having to reimplement platform specific stuff and we can have a C fallback.
I was excited about this till I read this: https://news.ycombinator.com/item?id=22090942
If the author is to be believed its just a transformation that is applied to the code. Basically the same transformation that we do with async/await already.
Now if this was like go-style coroutines I would be a lot more excited.