Re-implement allocation of base class subobjects.

Re-implement allocation of base class subobjects.

	* tree.c (unshare_base_binfos): New fn.
	(layout_basetypes): Use it.  Now handles offsets of both virtual and
	non-virtual bases, after layout_type.
	(layout_vbasetypes): Remove.
	(build_base_fields): Generate FIELD_DECLs for each non-virtual base.
	(build_vbase_pointer_fields): Split out from old layout_basetypes.
	* class.c (finish_base_struct): Lose offset handling code.
	Move nonvdtor warning here.  Don't mess with t_binfo anymore.
	(finish_struct_1): Don't mess with t_binfo anymore.  Use fns above.
	* cp-tree.h: Adjust.

From-SVN: r18973