fix compiler warning in posix winsync code for posix_group_del_memberuid_callback
(cherry picked from commit f440e039a5f2a7b2ea0dd087d8e91c554abc1be0)
(cherry picked from commit 761d9d550ca1025293dc1607760adea38ddc5452)
(cherry picked from commit 9750ea73014b36349040e166a469ed09236c2549)