message: Get Linux cross compile tools from our own GCS.
  Not sure why the normal download link isn't working from Travis. Maybe
  it's blocked?
diff: echo "Downloading Linux toolchain"
  -http --download https://cdn.unrealengine.com/CrossToolchain_Linux/v19_clang-11.0.1-centos7.exe
  +AWS_ACCESS_KEY_ID=${GOOGLE_ACCESS_KEY_ID} AWS_SECRET_ACCESS_KEY=${GOOGLE_SECRET_ACCESS_KEY} aws s3 --endpoint-url https://storage.googleapis.com cp s3://cesium-unreal-engine/4.27.0/Windows/v19_clang-11.0.1-centos7.exe .
  echo "Finished download"
  chmod a+x v19_clang-11.0.1-centos7.exe
  ./v19_clang-11.0.1-centos7.exe "//S"
  