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

[NohHyeon Kwon via cfe-commits]

swote-git wrote:

@Sirraide Thanks for your review! 

Should I move this to clang/test/CXX/drs/cwg1436.cpp and format it according to the DR test conventions?

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