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

[Aaron Ballman via cfe-commits]

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@@ -42,7 +42,12 @@ void p3example() {
   static auto y = 0.0;
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AaronBallman wrote:

This line should also be diagnosed in C++98 mode... this seems to be a preexisting bug: https://godbolt.org/z/3cza618cx (we have a similar bug with `register`: https://godbolt.org/z/zs5918YY4)

GitHub is too useless to let me put this comment on the correct line, but line 40 has a similar C++98 bug: https://godbolt.org/z/xEozMhe6z because there's no type specifier there, and line 41 does as well for the same reason.

Hmmm, it seems we're treating type deduction as an extension in C++98 mode, but we don't list it in the language extensions page as such and we don't issue pedantic diagnostics for it. @zygoloid do you recall if this was an intentional extension or not? Regardless, because this is existing behavior, nothing needs to change as part of this PR.

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