Hi SG10,

We currently have the feature test macro __cpp_coroutines, but we have no
macro for the library machinery in <coroutine>. I'm not super familiar with
coroutines, but it seems like this works a lot like <=> and <compare> where
you need the library bit to do anything?

Should we then change the language macro to __cpp_impl_coroutines and
introduce a new library macro __cpp_lib_coroutines, that users check for?

Barry