Add copyright headers to new files

Summary:
Copyright header was missing from cmake files and Open Source Bot complained
about it. Adding header to be compliant with our oss policies

Reviewed By: yns88

Differential Revision: D14603978

fbshipit-source-id: fab9e781969e10038537ebbdab87b1272f093bf1

build/fbcode_builder/CMake/FindGflags.cmake

+# Copyright (c) Facebook, Inc. and its affiliates.
 # Find libgflags.
 # There's a lot of compatibility cruft going on in here, both
 # to deal with changes across the FB consumers of this and also

build/fbcode_builder/CMake/FindGlog.cmake

+# Copyright (c) Facebook, Inc. and its affiliates.
 # - Try to find Glog
 # Once done, this will define
 #

build/fbcode_builder/CMake/FindLibEvent.cmake

+# Copyright (c) Facebook, Inc. and its affiliates.
 # - Find LibEvent (a cross event library)
 # This module defines
 # LIBEVENT_INCLUDE_DIR, where to find LibEvent headers

build/fbcode_builder/CMake/FindPCRE.cmake

+# Copyright (c) Facebook, Inc. and its affiliates.
 include(FindPackageHandleStandardArgs)
 find_path(PCRE_INCLUDE_DIR NAMES pcre.h)
 find_library(PCRE_LIBRARY NAMES pcre)

build/fbcode_builder/CMake/ThriftCppLibrary.cmake

+# Copyright (c) Facebook, Inc. and its affiliates.
 # NOTE: If you change this file, fbcode/fboss/github/ThriftCppLibrary.cmake also
 # needs to be changed.  TODO: this should be handled via shipit.
 function(add_thrift_cpp2_library LIB_NAME THRIFT_FILE)