CI is currently failing with new builds of clang due to a warning that std::experimental::coroutine_traits is deprecated, but libc++ does not have <coroutine> yet.
This looks related to D108696, which is already reverted out of main (thanks @ldionne).
Anyway, surely if we want to give a warning about <experimental/coroutine>, we should do it by putting a #warning directive in libc++'s <experimental/coroutine> itself; there is no reason for the compiler to be warning here, is there?
Is there something we can do to bump the compiler version on the CI then? It's a lot of work to confirm that these are the only failures. It looks like they're failing on Runtimes, MacOS x86_64, and the Apple back-deployment workers.