add test t5440 for patmat check

Author: liufengyun

tests/patmat/t5440.check

@@ -1,5 +1,5 @@
-./tests/patmat/t5440.scala:3: warning: match may not be exhaustive.
-It would fail on the following input: { (Nil, List(_)), (List(_), Nil) }
-    (list1, list2) match  {
-    ^
+./tests/patmat/t5440.scala:2: warning: match may not be exhaustive.
+It would fail on the following input: (Nil, List(_)), (List(_), Nil)
+  def merge(list1: List[Long], list2: List[Long]): Boolean = (list1, list2) match {
+                                                                            ^
 one warning found

tests/patmat/t5440.scala

@@ -0,0 +1,6 @@
+object Test {
+  def merge(list1: List[Long], list2: List[Long]): Boolean = (list1, list2) match {
+    case (hd1::_, hd2::_) => true
+    case (Nil, Nil) => true
+  }
+}