c++, coroutines: Simplify initial_await_resume_called.

c++, coroutines: Simplify initial_await_resume_called.

We do not need to generate this code early, since it does not affect
any of the analysis.  Lowering it later takes less code, and avoids
modifying the initial await expresssion which will simplify changes
to analysis to deal with open PRs.

gcc/cp/ChangeLog:

	* coroutines.cc (expand_one_await_expression): Set the
	initial_await_resume_called flag here.
	(build_actor_fn): Populate the frame accessor for the
	initial_await_resume_called flag.
	(cp_coroutine_transform::wrap_original_function_body): Do
	not modify the initial_await expression to include the
	initial_await_resume_called flag here.

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