[clang] [Clang] use parent declaration context to avoid asserting cast failure in defaulted comparison method (PR #96228)

[Shafik Yaghmour via cfe-commits]

https://github.com/shafik commented:

Thank you for the fix.

I am curious what specifically about this code triggers the crash. We do have a test w/ a defaulted outside the class. So there is another condition needed to trigger this. It looks like removing `constexpr` from `operator==(d h, g i)` prevents the crash.

Once we understand the specific condition we should add that to the summary.

https://github.com/llvm/llvm-project/pull/96228