[BUILD] auth: don't use unnamed unions

unnamed unions are not compatible with older compilers (eg: gcc 2.95) so
name it "u" instead.
diff --git a/include/types/auth.h b/include/types/auth.h
index d278de6..f7e3dd6 100644
--- a/include/types/auth.h
+++ b/include/types/auth.h
@@ -36,11 +36,9 @@
 	struct list list;
 	struct acl_cond *cond;			/* acl condition to meet */
 	unsigned int action;
-		union {
-			struct {
-			char *realm;
-		} http_auth;
-	};
+	struct {
+		char *realm;
+	} http_auth;
 };
 
 struct auth_users {
@@ -50,7 +48,7 @@
 	union {
 		char *groups;
 		unsigned int group_mask;
-	};
+	} u;
 };
 
 struct userlist {
diff --git a/src/auth.c b/src/auth.c
index 4740ca4..93af8d6 100644
--- a/src/auth.c
+++ b/src/auth.c
@@ -208,7 +208,7 @@
 	 * if user matches but group does not,
 	 * it makes no sens to check passwords
 	 */
-	if (group_mask && !(group_mask & u->group_mask))
+	if (group_mask && !(group_mask & u->u.group_mask))
 		return 0;
 
 	if (!(u->flags & AU_O_INSECURE)) {
diff --git a/src/cfgparse.c b/src/cfgparse.c
index a30a887..0b165e6 100644
--- a/src/cfgparse.c
+++ b/src/cfgparse.c
@@ -4223,7 +4223,7 @@
 				cur_arg += 2;
 				continue;
 			} else if (!strcmp(args[cur_arg], "groups")) {
-				newuser->groups = strdup(args[cur_arg + 1]);
+				newuser->u.groups = strdup(args[cur_arg + 1]);
 				cur_arg += 2;
 				continue;
 			} else {
@@ -5110,10 +5110,10 @@
 			unsigned int group_mask = 0;
 			char *group = NULL;
 
-			if (!curuser->groups)
+			if (!curuser->u.groups)
 				continue;
 
-			while ((group = strtok(group?NULL:curuser->groups, ","))) {
+			while ((group = strtok(group?NULL:curuser->u.groups, ","))) {
 
 				for (g = 0; g < curuserlist->grpcnt; g++)
 					if (!strcmp(curuserlist->groups[g], group))
@@ -5129,8 +5129,8 @@
 				group_mask |= (1 << g);
 			}
 
-			free(curuser->groups);
-			curuser->group_mask = group_mask;
+			free(curuser->u.groups);
+			curuser->u.group_mask = group_mask;
 		}
 
 		for (g = 0; g < curuserlist->grpcnt; g++) {
@@ -5151,7 +5151,7 @@
 					goto out;
 				}
 
-				curuser->group_mask |= (1 << g);
+				curuser->u.group_mask |= (1 << g);
 			}
 
 			free(curuserlist->groupusers[g]);