tests/lint: add test for incompatible pointer types in return

tests/usr.bin/xlint/lint1/msg_184.c

@@ -1,7 +1,10 @@
-/*	$NetBSD: msg_184.c,v 1.2 2021/02/21 09:07:58 rillig Exp $	*/
+/*	$NetBSD: msg_184.c,v 1.3 2021/03/19 08:01:58 rillig Exp $	*/
 # 3 "msg_184.c"
 
 // Test for message: illegal pointer combination [184]
 
-TODO: "Add example code that triggers the above message." /* expect: 249 */
-TODO: "Add example code that almost triggers the above message."
+int *
+example(char *cp)
+{
+	return cp;		/* expect: 184 */
+}

tests/usr.bin/xlint/lint1/msg_184.exp

@@ -1 +1 @@
-msg_184.c(6): syntax error ':' [249]
+msg_184.c(9): warning: illegal pointer combination [184]