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

[Vlad Serebrennikov via cfe-commits]

Endilll wrote:

So my takeaways here are:
1. Tests that ensure we don't crash anymore are important for us.
2. `-verify` is an acceptable way to write such tests.

Is this correct?

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