C++'s template-based sorting mechanisms allow for the same optimization without manually special-casing anything. (The compiler "integrates everything", to quote the author, out of the box.) C++ port of Postgresql, anyone?
Only if you actually can special case it automatically during compilation. It could still require a few tricks if your comparison comes from a user-defined query. At a minimum it would have to be something like: figure out which column type are you using, figure out what basic type does it map to, use that type in the template.
PostgreSQL is extensible enough that runtime specialisation would be best, I think. A JIT compiler, or a compiled type-safe multi-stage[1] programming language like MetaOCaml, would give the best performance.