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

[Vlad Serebrennikov via cfe-commits]

Endilll wrote:

I'd love if this PR added tests for Core issues 1436 and 3017, but I don't see which wording we should test against. The only proposed resolution from 2012-02 from Richard is obviously incomplete.

I think we shouldn't touch DR tests until more information from Core.

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