[clang] [clang-format] Use double hyphen for multiple-letter flags (PR #100978)

[Björn Schäpers via cfe-commits]

https://github.com/HazardyKnusperkeks requested changes to this pull request.

You certainly can add the double hyphen flags, but you can't remove the single ones.

https://github.com/llvm/llvm-project/pull/100978