message: clang-format: use style Google; always format all files.
  * -style=file does not seem to work in CI; more investigation
  needed. For now: use Google style explicitly.
  * Always format all files in repo to avoid corner-cases
  with git branches.
diff: FORMAT_OUT=${TMPDIR:-/tmp}/clang-format-diff.out
  -# Run on all the files that are affected
  -clang-format -i --style=file $(git diff --name-only --diff-filter=AM -r origin/master | grep '\(\.cc\|\.h\)$') 2> /dev/null
  +# Run on all files.
  +find . -name "*.h" -o -name "*.cc" -print0 \
  + | xargs -0 -P 2 clang-format --style=Google -i
  # Check if we got any diff
  git diff > ${FORMAT_OUT}
  