Include -haddock in DynFlags fingerprint

The -haddock flag determines whether or not the resulting .hi files
contain haddock documentation strings. If the existing .hi files do
not contain haddock documentation strings and the user requests them,
we should recompile.

Author: FinleyMcIlwaine

compiler/GHC/Driver/Flags.hs

@@ -568,6 +568,7 @@ codeGenFlags = EnumSet.fromList
      -- Flags that affect generated code
    , Opt_ExposeAllUnfoldings
    , Opt_NoTypeableBinds
+   , Opt_Haddock
 
      -- Flags that affect catching of runtime errors
    , Opt_CatchNonexhaustiveCases