Changes to ghc

Changes to ghc:
commit e577a52363ee7ee8a07f1d863988332ae8fbf2e4
Author: Simon Marlow <marlowsd@gmail.com>
Date:   Fri Jun 6 09:52:13 2014 +0100

    Fix discarding of unreachable code in the register allocator (#9155)

    A previous fix to this was wrong: f5879acd018494b84233f26fba828ce376d0f81d
    and left some unreachable code behind.  So rather than try to be clever and
    do this at the same time as the strongly-connected-component analysis, I'm
    doing a separate reachability pass first.