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

[Aaron Ballman via cfe-commits]

AaronBallman 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?

Yup, that's it exactly!

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