[GHC] #9623: Use Data.List.dropWhileEnd

[GHC]

#9623: Use Data.List.dropWhileEnd
-------------------------------------+-------------------------------------
              Reporter:  dfeuer      |            Owner:
                  Type:  task        |           Status:  new
              Priority:  normal      |        Milestone:  7.10.1
             Component:  libraries   |          Version:  7.8.3
  (other)                            |         Keywords:
            Resolution:              |     Architecture:  Unknown/Multiple
      Operating System:              |       Difficulty:  Easy (less than 1
  Unknown/Multiple                   |  hour)
       Type of failure:              |       Blocked By:
  None/Unknown                       |  Related Tickets:
             Test Case:              |
              Blocking:              |
Differential Revisions:              |
-------------------------------------+-------------------------------------

Comment (by thomie):

 Last time I tried 7.6 did not even compile 7.9, so I believe you can skip
 that.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9623#comment:4>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler