This change makes all non-user-creatable structures non-comparable. This
makes it easier to add changes later that don't introduce breaking
changes from the go compatibility guarantees perspective.
This, of course, implies that this change _is_ a breaking change, but since
these structures are not intended to be created by users (or de-referenced),
it should be okay.
(cherry picked from commit dbe032c347)
lhchavez
Carlos Martín Nieto
Han-Wen Nienhuys
Quinn Slack