c++, coroutines: Look through initial_await target exprs [PR110635].

c++, coroutines: Look through initial_await target exprs [PR110635].

In the case that the initial awaiter returns an object, the initial await
can be a target expression and we need to look at its initializer to cast
the await_resume() to void and to wrap in a compound expression that sets
the initial_await_resume_called flag.

	PR c++/110635

gcc/cp/ChangeLog:

	* coroutines.cc
	(cp_coroutine_transform::wrap_original_function_body): Look through
	initial await target expressions to find the actual co_await_expr
	that we need to update.

gcc/testsuite/ChangeLog:

	* g++.dg/coroutines/pr110635.C: New test.

Signed-off-by: Iain Sandoe <iain@sandoe.co.uk>