[C++20] [Coroutines] Disable to take the address of labels in coroutines

[C++20] [Coroutines] Disable to take the address of labels in coroutines

Closing https://github.com/llvm/llvm-project/issues/56436

We can't support the GNU address of label extension in coroutines well
in current architecture. Since the coroutines are going to split into
pieces in the middle end so the address of labels are ambiguous that
time.

To avoid any further misunderstanding, we try to emit an error here.

Differential Revision: https://reviews.llvm.org/D131938