Add missing copyright headers

Reviewed By: AhmedSoliman

Differential Revision: D15060131

fbshipit-source-id: 428f50129ec79c0f6091829dc5946163e532cde1

build/fbcode_builder/CMake/FindGMock.cmake

-#
+# Copyright (c) Facebook, Inc. and its affiliates.
 # Find libgmock
 #
 #  LIBGMOCK_DEFINES     - List of defines when using libgmock.

build/fbcode_builder/docker_enable_ipv6.sh

 #!/bin/sh
+# Copyright (c) Facebook, Inc. and its affiliates.
 
 
 # `daemon.json` is normally missing, but let's log it in case that changes.