[clang] [Clang] Coroutines: Properly Check if `await_suspend` return type convertible to `std::coroutine_handle<>` (PR #85684)

[Chuanqi Xu via cfe-commits]

ChuanqiXu9 wrote:

> I am also ok with changing the patch to reject programs whose await_suspend doesn't strictly return std::coroutine_handle if upstream prefers.

It should be good to do that since it makes the behavior more conforming. And maybe it is better to do this a seperate patch.
Especially if it can help reduce the many non-semantical changes in SemaExprCXX.cpp.



https://github.com/llvm/llvm-project/pull/85684