[clang] [clang] add test verifying DR242 behavior (PR #201441)

[Vlad Serebrennikov via cfe-commits]

https://github.com/Endilll commented:

You need to run `clang/www/make_cxx_dr_status`, and include changes for CWG242 that will come out of it. This should be good to go after that.

https://github.com/llvm/llvm-project/pull/201441