test: expand switch dead code test to include a range

Change-Id: If443ffb50b140c466dcf4cc5340f44948bfa46a9
Reviewed-on: https://go-review.googlesource.com/26765
Reviewed-by: Matthew Dempsky <mdempsky@google.com>

test/fixedbugs/issue9608.dir/issue9608.go

@@ -67,6 +67,15 @@ func init() {
 	case true:
 		fail()
 	}
+
+	// Test dead code elimination in large ranges.
+	switch 5 {
+	case 3, 4, 5, 6, 7:
+	case 0, 1, 2:
+		fail()
+	default:
+		fail()
+	}
 }
 
 func main() {