[clang] [clang][test] Add test for comma operator rejection in preprocessor conditionals (PR #155570)

[Vlad Serebrennikov via cfe-commits]

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+// RUN: %clang_cc1 -E -pedantic-errors %s -verify -std=c++98
+// RUN: %clang_cc1 -E -pedantic-errors %s -verify -std=c++11
+// RUN: %clang_cc1 -E -pedantic-errors %s -verify -std=c++14
+// RUN: %clang_cc1 -E -pedantic-errors %s -verify -std=c++17
+// RUN: %clang_cc1 -E -pedantic-errors %s -verify -std=c++20
+// RUN: %clang_cc1 -E -pedantic-errors %s -verify=expected,embed -std=c++23 -Wno-c23-extensions
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Endilll wrote:

```suggestion
// RUN: %clang_cc1 -E -pedantic-errors %s -verify=expected,since-cxx23 -std=c++23 -Wno-c23-extensions
```
This would follow the prefixes that C++ DR tests are using

https://github.com/llvm/llvm-project/pull/155570