[libc++] Specialize __lazy_synth_three_way_comparator for std::greater and friends (#157624)
This specializes `__lazy_synth_three_way_comparator` to forward to
`__default_three_way_comparator` if the comparator desugars to
`__greater_tag`. This is the same as the desugaring to `__less_tag`
except that the sign has to be inverted.