gc: test that asserts closures are not wrapped when they don't have closure vars.

R=rsc, bradfitz
CC=golang-dev
https://golang.org/cl/5529060

test/closure.go

@@ -6,6 +6,8 @@
 
 package main
 
+import "runtime"
+
 var c = make(chan int)
 
 func check(a []int) {
@@ -77,6 +79,8 @@ func h() {
 func newfunc() func(int) int { return func(x int) int { return x } }
 
 func main() {
+	var fail bool
+
 	go f()
 	check([]int{1, 4, 5, 4})
 
@@ -88,13 +92,26 @@ func main() {
 	go h()
 	check([]int{100, 200, 101, 201, 500, 101, 201, 500})
 
+	runtime.UpdateMemStats()
+        n0 := runtime.MemStats.Mallocs
+
 	x, y := newfunc(), newfunc()
 	if x(1) != 1 || y(2) != 2 {
 		println("newfunc returned broken funcs")
-		panic("fail")
+		fail = true
+	}
+
+	runtime.UpdateMemStats()
+        if n0 != runtime.MemStats.Mallocs {
+		println("newfunc allocated unexpectedly")
+		fail = true
 	}
 
 	ff(1)
+
+	if fail {
+		panic("fail") 
+	}
 }
 
 func ff(x int) {