c++: Correct behaviour of layout_compatible_type for aligned types

c++: Correct behaviour of layout_compatible_type for aligned types

The standard does not require two types to have the same alignment (and
hence size) to be considered layout-compatible.  The same applies to
members of unions.

gcc/cp/ChangeLog:

	* typeck.cc (layout_compatible_type_p): Do not check TYPE_SIZE.

gcc/testsuite/ChangeLog:

	* g++.dg/cpp2a/is-layout-compatible3.C: Adjust expected results.

Signed-off-by: Nathaniel Shead <nathanieloshead@gmail.com>
Reviewed-by: Jason Merrill <jason@redhat.com>