[clang] [Clang] Fix -Wunused-private-field false negative with defaulted comparison operators (PR #116871)

[Mészáros Gergely via cfe-commits]

Maetveis wrote:

@whiteio You seem to have the [Keep my email addresses private](https://github.com/settings/emails) setting enabled in your account. This will make the merged commit reference `84482442+whiteio at users.noreply.github.com` if you'd like to use your actual address please disable this option.

https://github.com/llvm/llvm-project/pull/116871