[clang] [clang-format] Add --fail-on-incomplete-format. (PR #84346)

[Björn Schäpers via cfe-commits]

https://github.com/HazardyKnusperkeks commented:

I think you need to run `clang/docs/tools/dump_format_help.py`.

https://github.com/llvm/llvm-project/pull/84346