class.c (finish_struct_1): When copying the primary base's VFIELD, make sure we find it is at offset zero.

cp:
	* class.c (finish_struct_1): When copying the primary base's
	VFIELD, make sure we find it is at offset zero.
testsuite:
	* g++.dg/abi/vbase8-10.C: New test.

From-SVN: r44421