coroutines: Look through NOPs for awaiter variables [PR 99575].

coroutines: Look through NOPs for awaiter variables [PR 99575].

There was a missing STRIP_NOPS which meant that, in some cases,
an awaiter variable could be hidden by a view-convert-expr.

Signed-off-by: Iain Sandoe <iain@sandoe.co.uk>
	PR c++/99575

gcc/cp/ChangeLog:

	* coroutines.cc (build_co_await): Strip NOPs from
	candidate awaiter expressions before testing to see
	if they need a temporary.

gcc/testsuite/ChangeLog:

	* g++.dg/coroutines/pr99575.C: New test.