[clang][Sema] Emit more specific diagnostic for auto in lambda before C++14 (#46059) (#68540)

Namely, we specify that `auto` in a lambda parameter is a C++14
extension in the error message, which now reads:

`'auto' not allowed in lambda parameter before C++14`

This does not change the behavior for `decltype(auto)` and `__auto_type`
though.

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Co-authored-by: cor3ntin <corentinjabot@gmail.com>