* cp/class.c (contains_empty_class_p): New method.
	(walk_subobject_offsets): Correct computation of field offset.
	(layout_empty_base): Correct placement of emtpy base classes.
	(layout_class_type): Warn about ABI changes.

	* doc/invoke.texi: Add more -Wabi examples.

	* gcc/testsuite/g++.dg/abi/empty5.C: New test.
	* gcc/testsuite/g++.dg/abi/empty6.C: New test.
	* gcc/testsuite/g++.dg/abi/vbase12.C: New test.

From-SVN: r57508