Suppress orphan warning pre-GHC 7.8

Signed-off-by: Edward Z. Yang <ezyang@cs.stanford.edu>

Cabal/Distribution/Version.hs

 {-# LANGUAGE CPP, DeriveDataTypeable, StandaloneDeriving #-}
+#if __GLASGOW_HASKELL__ < 707
+{-# OPTIONS_GHC -fno-warn-orphans #-}
+#endif
 -----------------------------------------------------------------------------
 -- |
 -- Module      :  Distribution.Version