runtime, sync: add copyright headers to new files

For #38029

Change-Id: I71de2b66c1de617d32c46d4f2c1866f9ff1756ec
Reviewed-on: https://go-review.googlesource.com/c/go/+/244631
Run-TryBot: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Dan Scales <danscales@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>

src/runtime/lockrank_off.go

@@ -1,3 +1,7 @@
+// Copyright 2020 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.
+
 // +build !goexperiment.staticlockranking
 
 package runtime

src/runtime/lockrank_on.go

@@ -1,3 +1,7 @@
+// Copyright 2020 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.
+
 // +build goexperiment.staticlockranking
 
 package runtime

src/sync/runtime2.go

@@ -1,3 +1,7 @@
+// Copyright 2020 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.
+
 // +build !goexperiment.staticlockranking
 
 package sync

src/sync/runtime2_lockrank.go

@@ -1,3 +1,7 @@
+// Copyright 2020 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.
+
 // +build goexperiment.staticlockranking
 
 package sync