class.c: Change vtable to be more compatible with g++ v3 abi.

class.c: Change vtable to be more compatible with g++ v3 abi.

	*  class.c:  Change vtable to be more compatible with g++ v3 abi.
	(get_dispatch_table):  Prepend offset-to-top (always 0) and
	type_info pointer (currently unimplemented hence NULL) to vtable.
	Specifically, prepend offset-to-top and typeinfo ptr (currently null).
	(make_class_data):  Variable dtable_start_offset is sizeof 2 pointers.
	Adjust vtable pointers by dtable_start_offse - i.e. skip new words.
	(build_dtable_decl):  Add declarations for new fields.

From-SVN: r49978