chromiumDev: Add the missing clang-format binary

The fix from 1d961a4c was unfortunately incomplete. This commit fixes
the second error [0] that occurs later during the build (the Python
script third_party/blink/renderer/bindings/scripts/generate_bindings.py
requires buildtools/linux64/clang-format).

[0]: https://github.com/NixOS/nixpkgs/pull/81016#issuecomment-591572821