```cmake
# Copyright 2018 Google LLC
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#      http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.

include(ExternalProject)

if(TARGET flatbuffers OR NOT DOWNLOAD_FLATBUFFERS)
  return()
endif()

set(version c957550511689e1052059fc2cf2e43a06a24a05b)

ExternalProject_Add(
  flatbuffers

  DOWNLOAD_DIR ${FIREBASE_DOWNLOAD_DIR}
  DOWNLOAD_NAME flatbuffers-${version}.tar.gz
  URL https://github.com/google/flatbuffers/archive/${version}.tar.gz

  PREFIX ${PROJECT_BINARY_DIR}

  CONFIGURE_COMMAND ""
  BUILD_COMMAND ""
  INSTALL_COMMAND ""
  TEST_COMMAND ""
)
```

Update Flatbuffers to include CPack fix
user
```cmake
# Copyright 2018 Google LLC
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#      http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.

include(ExternalProject)

if(TARGET flatbuffers OR NOT DOWNLOAD_FLATBUFFERS)
  return()
endif()

set(version 97ffc590e336b800d346bdf2f4876394bb353f97)

ExternalProject_Add(
  flatbuffers

  DOWNLOAD_DIR ${FIREBASE_DOWNLOAD_DIR}
  DOWNLOAD_NAME flatbuffers-${version}.tar.gz
  URL https://github.com/google/flatbuffers/archive/${version}.tar.gz

  PREFIX ${PROJECT_BINARY_DIR}

  CONFIGURE_COMMAND ""
  BUILD_COMMAND ""
  INSTALL_COMMAND ""
  TEST_COMMAND ""
)
```
assistant