Add StandaloneDeriving extension

Distribution/Compiler.hs

@@ -206,6 +206,9 @@ extensionsToGHCFlag v l
     extensionToGHCFlag e@TypeFamilies
      | v >= v6_7 = Right "-XTypeFamilies"
      | otherwise = Left e
+    extensionToGHCFlag e@StandaloneDeriving
+     | v >= v6_7 = Right "-XStandaloneDeriving"
+     | otherwise = Left e
 
     extensionToGHCFlag e@ExtensibleRecords          = Left e
     extensionToGHCFlag e@RestrictedTypeSynonyms     = Left e

Language/Haskell/Extension.hs

@@ -91,4 +91,5 @@ data Extension
   | HereDocuments
   | MagicHash
   | TypeFamilies
+  | StandaloneDeriving
   deriving (Show, Read, Eq)