[GHC] #9727: -Werror=unused-but-set-variable causes validation error on Windows

[GHC]

#9727: -Werror=unused-but-set-variable causes validation error on Windows
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              Reporter:  gintas      |            Owner:  gintas
                  Type:  bug         |           Status:  new
              Priority:  normal      |        Milestone:
             Component:  Build       |          Version:  7.9
  System                             |         Keywords:
            Resolution:              |     Architecture:  Unknown/Multiple
      Operating System:  Windows     |       Difficulty:  Unknown
       Type of failure:  Building    |       Blocked By:
  GHC failed                         |  Related Tickets:
             Test Case:              |
              Blocking:              |
Differential Revisions:  Phab:D373   |
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Changes (by gintas):

 * differential:   => Phab:D373


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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9727#comment:1>
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