[clang] Fix crash on defaulted comparison recovery in Sema and AST (PR #210668)

[purnima shrivastava via cfe-commits]

purnima-nlp wrote:

> I think the fix for this should be in DefineDefaultedComparison -- gating on the class definition being completed maybe?

Yes sir, I'm looking on this issue

https://github.com/llvm/llvm-project/pull/210668