runtime: get more info for TestCgoSignalDeadlock failures

Updates #18598

Change-Id: I13c60124714cf9d1537efa0a7dd1e6a0fed9ae5b
Reviewed-on: https://go-review.googlesource.com/46723
Run-TryBot: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

src/runtime/testdata/testprogcgo/cgo.go

@@ -45,10 +45,13 @@ func CgoSignalDeadlock() {
 				}()
 				var s *string
 				*s = ""
+				fmt.Printf("continued after expected panic\n")
 			}()
 		}
 	}()
 	time.Sleep(time.Millisecond)
+	start := time.Now()
+	var times []time.Duration
 	for i := 0; i < 64; i++ {
 		go func() {
 			runtime.LockOSThread()
@@ -62,16 +65,17 @@ func CgoSignalDeadlock() {
 		ping <- false
 		select {
 		case <-ping:
+			times = append(times, time.Since(start))
 		case <-time.After(time.Second):
-			fmt.Printf("HANG\n")
+			fmt.Printf("HANG 1 %v\n", times)
 			return
 		}
 	}
 	ping <- true
 	select {
 	case <-ping:
 	case <-time.After(time.Second):
-		fmt.Printf("HANG\n")
+		fmt.Printf("HANG 2 %v\n", times)
 		return
 	}
 	fmt.Printf("OK\n")