coroutines: Fix ICE with an invalid await_suspend type [PR100673].

coroutines: Fix ICE with an invalid await_suspend type [PR100673].

The reported ICE occurs when an invalid (non-template) type is found
as the return for an await_suspend.

Fixed by amending build_co_await to ensure that await_suspend return-
type is a template-instantiation before checking to see if it is a
valid coroutine handle type.

Signed-off-by: John Eivind Helset <jehelset@gmail.com>
Signed-off-by: Iain Sandoe <iain@sandoe.co.uk>
	PR c++/100673

gcc/cp/ChangeLog:

	* coroutines.cc (build_co_await): Guard against NULL
	await_suspend types.

gcc/testsuite/ChangeLog:

	* g++.dg/coroutines/pr100673.C: New test.