runtime: deflake TestCgoCheckBytes

Bump up the multiplier to 20.  Also run the fast version first, so that
the slow version is likely to start up faster.

Change-Id: Ia0654cc1212ab03a45da1904d3e4b57d6a8d02a0
Reviewed-on: https://go-review.googlesource.com/19835
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Minux Ma <minux@golang.org>

src/runtime/crash_cgo_test.go

@@ -162,19 +162,19 @@ func TestCgoCheckBytes(t *testing.T) {
 	}
 
 	cmd := testEnv(exec.Command(exe, "CgoCheckBytes"))
+	cmd.Env = append(cmd.Env, "GODEBUG=cgocheck=0")
 
 	start := time.Now()
 	cmd.Run()
 	d1 := time.Since(start)
 
 	cmd = testEnv(exec.Command(exe, "CgoCheckBytes"))
-	cmd.Env = append(cmd.Env, "GODEBUG=cgocheck=0")
 
 	start = time.Now()
 	cmd.Run()
 	d2 := time.Since(start)
 
-	if d2*10 < d1 {
+	if d1*20 < d2 {
 		t.Errorf("cgo check too slow: got %v, expected at most %v", d1, d2*10)
 	}
 }