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

[Shafik Yaghmour via cfe-commits]

shafik wrote:

> @shafik was https://www.open-std.org/jtc1/sc22/wg21/docs/cwg_active.html#3017 resolved ?

No, it is still active. It looks like [CWG1436](https://www.open-std.org/jtc1/sc22/wg21/docs/cwg_active.html#1436) is where the action will be moving forward.

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