Specifically, with
clang-format --style='{ IndentWidth: 4, BreakBeforeBraces: Mozilla, ColumnLimit: 120, PointerAlignment: Middle }'
which was the clang-format invocation that produced the fewest diffs on
the nix source out of ~20 that I tried.
Also add --all, which shows the value of all options. Diffing the --all
output on either side of contemplated changes is a lovely way to better
understand what's going on inside nixos.