Implement checkable "minimal complete definitions" (#7633)
This commit adds a `{-# MINIMAL #-}` pragma, which defines the possible minimal complete definitions for a class. The body of the pragma is a boolean formula of names. The old warning for missing methods is replaced with this new one. Note: The interface file format is changed to store the minimal complete definition. Authored-by:Twan van Laarhoven <twanvl@gmail.com> Signed-off-by:
Herbert Valerio Riedel <hvr@gnu.org>