Libc++ coroutines are production ready!
But seriously, the library implementation for coroutines is just a shallow wrapper around compiler builtins.
Therefore libc++ is probably bug free, but Clang certainly isn't.
EDIT: "probably bug free" == famous last words.
John Bandela had a great talk about that at CppCon 2016: "Channels - An alternative to callbacks and futures" [0]
Interesting time for all we C++ fans.