[clang] [Clang] Accept auto parameters pre-C++20 as an extension (PR #200670)

[Nikolas Klauser via cfe-commits]

philnik777 wrote:

> Documentation CI failures are unrelated; changes LGTM but for the future, please use git-clang-format to format only the parts of your PR which are being changed (there's quite a bit of unrelated changes which make review harder).

This isn't clang-format, but the editor simply removing trailing whitespace.

https://github.com/llvm/llvm-project/pull/200670