c++, coroutines: Make a check more specific [PR109283].

c++, coroutines: Make a check more specific [PR109283].

The check was intended to assert that we had visited contained
ternary expressions with embedded co_awaits, but had been made
too general - and therefore was ICEing on code that was actually
OK.  Fixed by checking specifically that no co_awaits embedded.

	PR c++/109283

gcc/cp/ChangeLog:

	* coroutines.cc (find_any_await): Only save the statement
	pointer if the caller passes a place for it.
	(flatten_await_stmt): When checking that ternary expressions
	have been handled, also check that they contain a co_await.

gcc/testsuite/ChangeLog:

	* g++.dg/coroutines/pr109283.C: New test.

Signed-off-by: Iain Sandoe <iain@sandoe.co.uk>
(cherry picked from commit 977fadd69776e2a8a6daca43e1c898bc4f87154d)