Tags aren't generated for GADT constructors with :: on different line

[ntc2]

For example, in what follows we only get tags for C1 and C3, and not for ThisConstructorNameIsLongSoImPuttingTheTypeOnTheNextLine:

{-# LANGUAGE GADTs #-}
data D a where
  C1 :: Int -> D Int
  ThisConstructorNameIsLongSoImPuttingTheTypeOnTheNextLine
    :: Int -> Bool -> D String
  C3 :: Int
     -> Bool
     -> D Int

This is in the same vein as Issues #16 and #40.