Auto-derive a few manually coded Show instances

In `base`, the instances

  instance Show ()
  instance Show Bool
  instance Show Ordering
  instance Show a => Show (Maybe a)

where defined manually, even though we can leverage GHC's auto-deriver
which is perfectly capable by standalone derivation to avoid boiler-plate
code such as this.

Reviewed By: austin

Differential Revision: https://phabricator.haskell.org/D219