Changes to ghc

Changes to ghc:
commit ab105f83dcd5f9094a9edb0f0c8266fba6f3c808
Author: Edward Z. Yang <ezyang@cs.stanford.edu>
Date:   Thu Jun 26 16:52:52 2014 +0100

    Add new flag -fwrite-interface for -fno-code.

    Summary:
    Normally, -fno-code does not generate interface files.
    However, if you want to use it to type check over multiple
    runs of GHC, you will need the interface files to check
    source files further down the dependency chain; -fwrite-interface
    does this for you.

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

    Test Plan: clean validate, and a new test-case

    Reviewers: simonpj

    Subscribers: simonmar, relrod, carter

    Differential Revision: https://phabricator.haskell.org/D27