[clang] use correct builtin type for defaulted comparison analyzer

Fixes PR50591.

When analyzing classes with members which have user-defined conversion
operators to builtin types, the defaulted comparison analyzer was
picking the member type instead of the type for the builtin operator
which was selected as the best match.

This could either result in wrong comparison category being selected,
or a crash when runtime checks are enabled.

Signed-off-by: Matheus Izvekov <mizvekov@gmail.com>

Reviewed By: rsmith

Differential Revision: https://reviews.llvm.org/D103760