[clang] [clang][Sema] Add checks for validity of default ctor's class (PR #78898)

[Mariya Podchishchaeva via cfe-commits]

Fznamznon wrote:

So, there is no way to consistently check on all platforms that we didn't crash when an error diagnostic was issued (does clang return non-zero when there is error diagnostic?), is that a right understanding?
Still, if the tests won't be "pretty" that is not an excuse to not add tests, IMO.

https://github.com/llvm/llvm-project/pull/78898