coroutines: Pass class ref to traits lookup and promise allocator [PR94760].

coroutines: Pass class ref to traits lookup and promise allocator [PR94760].

We changed the argument passed to the promise parameter preview
to match a reference to *this.  However to be consistent with the
other ports, we do need to match the reference transformation in
the traits lookup and the promise allocator lookup.

gcc/cp/ChangeLog:

2020-04-28  Iain Sandoe  <iain@sandoe.co.uk>

	PR c++/94760
	* coroutines.cc (instantiate_coro_traits): Pass a reference to
	object type rather than a pointer type for 'this', for method
	coroutines.
	(struct param_info): Add a field to hold that the parm is a lambda
	closure pointer.
	(morph_fn_to_coro): Check for lambda closure pointers in the
	args.  Use a reference to *this when building the args list for the
	promise allocator lookup.

gcc/testsuite/ChangeLog:

2020-04-28  Iain Sandoe  <iain@sandoe.co.uk>

	PR c++/94760
	* g++.dg/coroutines/pr94760-mismatched-traits-and-promise-prev.C:
	New test.