[clang] [Clang] prevent incorrect rejection of auto with reordered declaration specifiers in C23 (PR #177865)

[Oleksandr Tarasiuk via cfe-commits]

a-tarasyuk wrote:

@cor3ntin @AaronBallman Thank you for your feedback. I have updated the logic to use `isTypeSpecifierQualifier()`, with exception handling for the `_Atomic(` and `typeof(` forms. I am unsure whether `isKnownToBeTypeSpecifier()` should be extended for `_Atomic` or `typeof`, since it is unclear if it should recognize only the keyword or the keyword followed by `(`.

https://github.com/llvm/llvm-project/pull/177865