Address compiler warnings about type mismatch, seen on Travis. This p…

…articular

case is a platform-dependent one; let's assume that gid_t is the future,
rather than int, for GIDs.

modules/mod_auth_unix.c

@@ -1162,7 +1162,7 @@ static int get_groups_by_getgrouplist(const char *user, gid_t primary_gid,
     "using getgrouplist(3) to look up group membership");
 
   memset(group_ids, 0, sizeof(group_ids));
-  if (getgrouplist(user, primary_gid, (int *) group_ids, &ngroups) < 0) {
+  if (getgrouplist(user, primary_gid, group_ids, &ngroups) < 0) {
     int xerrno = errno;
 
     pr_log_pri(PR_LOG_WARNING, "getgrouplist(3) error: %s", strerror(xerrno));