[llvm] [clang] [Coroutines] Introduce [[clang::coro_only_destroy_when_complete]] (PR #71014)

[Chuanqi Xu via cfe-commits]

ChuanqiXu9 wrote:

@bcardosolopes @apolloww @rjmccall would you like to take a look for the middle end part?

https://github.com/llvm/llvm-project/pull/71014