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

[via cfe-commits]

github-actions[bot] wrote:

<!--PREMERGE ADVISOR COMMENT: Windows-->
# :window: Windows x64 Test Results

* 51560 tests passed
* 877 tests skipped
* 1 test failed

## Failed Tests
(click on a test name to see its output)

### Clang
<details>
<summary>Clang.Parser/c2x-auto.c</summary>

```
Exit Code: 1

Command Output (stdout):
--
# RUN: at line 1
c:\_work\llvm-project\llvm-project\build\bin\clang.exe -cc1 -internal-isystem C:\_work\llvm-project\llvm-project\build\lib\clang\22\include -nostdsysteminc -fsyntax-only -verify=expected,c23 -std=c23 C:\_work\llvm-project\llvm-project\clang\test\Parser\c2x-auto.c
# executed command: 'c:\_work\llvm-project\llvm-project\build\bin\clang.exe' -cc1 -internal-isystem 'C:\_work\llvm-project\llvm-project\build\lib\clang\22\include' -nostdsysteminc -fsyntax-only -verify=expected,c23 -std=c23 'C:\_work\llvm-project\llvm-project\clang\test\Parser\c2x-auto.c'
# .---command stderr------------
# | error: diagnostics with 'error' severity expected but not seen: 
# |   File C:\_work\llvm-project\llvm-project\clang\test\Parser\c2x-auto.c Line 147 'c23-error': illegal storage class on file-scoped variable
# | 1 error generated.
# `-----------------------------
# error: command failed with exit status: 1

--

```
</details>

If these failures are unrelated to your changes (for example tests are broken or flaky at HEAD), please open an issue at https://github.com/llvm/llvm-project/issues and add the `infrastructure` label.

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