Suggest -XGeneralizedNewtypeDeriving for newtypes

newtype A = A Int deriving Enum

t.hs:1:27:

Can't make a derived instance of Enum A' (A' has non-nullary constructors)

In the newtype declaration for `A'

But perhaps -XGeneralizedNewtypeDeriving should be suggested (ideally only if the wrapped type actually had such an instance)?

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