runtime: skip TestGdbBacktrace on netbsd

Also adds missing copyright notice.

Updates #15603.

Change-Id: Icf4bb45ba5edec891491fe5f0039a8a25125d168
Reviewed-on: https://go-review.googlesource.com/23501Reviewed-by: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

src/runtime/runtime-gdb_test.go

+// Copyright 2015 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
 package runtime_test
 
 import (
@@ -207,6 +211,10 @@ func TestGdbBacktrace(t *testing.T) {
 	checkGdbEnvironment(t)
 	checkGdbVersion(t)
 
+	if runtime.GOOS == "netbsd" {
+		testenv.SkipFlaky(t, 15603)
+	}
+
 	dir, err := ioutil.TempDir("", "go-build")
 	if err != nil {
 		t.Fatalf("failed to create temp directory: %v", err)