CPP pragma ignored if top comments and Opt_KeepRawTokenStream

HaRe sets Opt_KeepRawTokenStream to be able to round trip the source code.

If we have a module starting

{-

A normal comment, to check if we can still pick up the CPP directive after it.

-}
{-# LANGUAGE FlexibleInstances #-}
{-# LANGUAGE CPP #-}
-- Check that we can parse a file which requires CPP
module BCpp where
bob :: Int -> Int -> Int
#if __GLASGOW_HASKELL__ > 704
bob x y = x + y
#else
bob x y = x + y * 2
#endif

then the call to load LoadAllTargets via the GHC API fails with

SourceError (lexical error at character 'i' which is the normal error when #if is hit and CPP is not enabled.

If Opt_KeepRawTokenStream is not set it loads without problems.

Also, files using CPP but not having a top comment load properly too.