Define GHC.Types.Coercible

This data type is required so that Coercible (which is actually a class
and is exported from GHC.Prim) has a info table etc., similar to ~
Add `{-# MINIMAL #-}` to `class Eq` and `class Ord`

This makes use of the new compiler checked minimal-complete-defintion
`{-# MINIMAL #-}` annotation (see #7633 for more details)

Signed-off-by: Herbert Valerio Riedel <hvr@gnu.org>
Follow changes in comparison primops (see #6135)
Comments only