disable horrible tab warning, needed in every file that Setup.hs pulls in

This is certianly a cabal bug for not passing the build options in the
cabal file when building Setup.hs.

And, why oh why did ghc enable this warning by default? So unhappy with
this choice.

Utility/FileSystemEncoding.hs

@@ -6,6 +6,7 @@
  -}
 
 {-# LANGUAGE CPP #-}
+{-# OPTIONS_GHC -fno-warn-tabs #-}
 
 module Utility.FileSystemEncoding (
 	fileEncoding,