It's very tempting to write

auto set = BSONElementComparator(BSONElementComparator::FieldNamesMode::kIgnore,
                                 stringDataBinaryComparator)
                   .makeBSONEltSet();

but this would be wrong, as the BSONElementComparator must outlive the container. We should delete the rvalue ref-qualified versions of these functions to stop code like this from compiling.