Add license headers to all go files.

Required as of
https://chromium.git.corp.google.com/chromiumos/repohooks/+/9732e38a5551e4bbcd222d2bbb89ee0fc5c95dee

BUG=chromium:773875
TEST=unit test

Change-Id: I8dfed85b0fbd528084ff2e585bbf3624ac358135
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/third_party/toolchain-utils/+/1710404
Tested-by: Tobias Bosch <tbosch@google.com>
Reviewed-by: George Burgess <gbiv@chromium.org>
diff --git a/compiler_wrapper/errors.go b/compiler_wrapper/errors.go
index 8cf9634..18e0fac 100644
--- a/compiler_wrapper/errors.go
+++ b/compiler_wrapper/errors.go
@@ -1,3 +1,7 @@
+// Copyright 2019 The Chromium OS 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 main
 
 import (