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

[Björn Schäpers via cfe-commits]

HazardyKnusperkeks wrote:

Okay, I can't revoke my vote and remove me as reviewer. As demonstrated I'm not qualified to review python changes.

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