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

[Nikolas Klauser via cfe-commits]

philnik777 wrote:

> > Could you share what you have in mind here? for concepts you first kinda need the keywords, which we don't have pre-C++20.
> 
> Good point about not having the keyword.
> 
> Still, what does `void f(Foo auto)` do?

It gives a generic `unknown type name 'Foo'`. Do you think that's worth adding somewhere?

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