[GHC] #10511: Simplify some preprocessor expressions

[GHC]

#10511: Simplify some preprocessor expressions
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              Reporter:  Berdes      |             Owner:  Berdes
                  Type:  task        |            Status:  new
              Priority:  low         |         Milestone:
             Component:  Compiler    |           Version:  7.10.1
              Keywords:              |  Operating System:  Unknown/Multiple
          Architecture:              |   Type of failure:  None/Unknown
  Unknown/Multiple                   |        Blocked By:
             Test Case:              |   Related Tickets:
              Blocking:              |
Differential Revisions:              |
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 Some proprocessor expressions can be simplified. For exemple, when
 `_MSC_VER` is defined, `_WIN32` is also defined.

 So `#if defined(_MSC_VER) || defined(_WIN32)` can be simplified to `#if
 defined(_WIN32)`.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10511>
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