[clang] Add test for CWG1397

Resolution of this CWG breaks potential dependency loop between complete-class context of non-static data member initializer (NSDMI), and defaulted default constructor, which is `noexcept` depending on NSDMIs among other things.

For whatever reason in C++11 mode we issue an additional note and a different line number for the primary error. But I find the message itself even worse than aforementioned issues. It describes what's going on, but doesn't say what's bad about it. I find the previous version of this message more clear: https://github.com/llvm/llvm-project/commit/8dbc6b26171167b8ddf66a5f4b6d6fb9baf28336 . Created an issue for that: #62823

Reviewed By: #clang-language-wg, shafik

Differential Revision: https://reviews.llvm.org/D151034