Fix Travis failures on older GHCs.

Author: merijn

Cabal/Distribution/Simple/Flag.hs

@@ -1,4 +1,5 @@
 {-# LANGUAGE DeriveGeneric #-}
+{-# LANGUAGE FlexibleContexts #-}
 -----------------------------------------------------------------------------
 -- |
 -- Module      :  Distribution.Simple.Flag

Cabal/Distribution/Simple/Program/GHC.hs

@@ -35,7 +35,6 @@ import Distribution.Simple.Program.Run
 import Distribution.System
 import Distribution.Text
 import Distribution.Types.ComponentId
-import Distribution.Types.Library (libBuildInfo)
 import Distribution.Verbosity
 import Distribution.Version
 import Distribution.Utils.NubList