[clang] [clang] Reject 'auto' storage class with type specifier in C++ (PR #166004)

[Osama Abdelkader via cfe-commits]

osamakader wrote:

Thanks @to268, can we merge this PR cleanly? or should I resolve the conflicts in (ReleaseNotes.rst, p3-generic-lambda-1y.cpp test) first?

https://github.com/llvm/llvm-project/pull/166004