Description:add copyright statement for Build.gn
Team:OTHERS
Feature or Bugfix:Bugfix
Binary Source:No
PrivateCode(Yes/No):No

Change-Id: Id0a6bec931218dde977f6273e165cd2e9d23f7b5
Reviewed-on: http://mgit-tm.rnd.huawei.com/9705303Tested-by: Npublic jenkins <public_jenkins@notesmail.huawei.com>
Reviewed-by: Nhouyuezhou 00386575 <hou@huawei.com>
Reviewed-by: Npuxing 00257459 <puxing@huawei.com>