In 89089, we were never actually setting DECL_SIZE on an empty data member,
because its type is a POD, so we didn't set it in the maybe-overlapping
section.  Fixed by also handling empty types there.

In 88865, we were failing to consider empty data members in
include_empty_classes.  Fixed by making end_of_class always include them.

While looking at these I noticed that the ABI says that a
potentially-overlapping data member makes its class non-layout-POD, and that
an empty data member doesn't prevent its class from being empty, so I've
implemented those points as well.

	PR c++/88865 - wrong layout with [[no_unique_address]].
	* class.c (check_field_decls): A potentially-overlapping field makes
	the class non-layout-POD, but not non-empty.
	(end_of_class): Always consider empty data members.
	(layout_class_type): Set DECL_SIZE for empty fields.

From-SVN: r268368