[GHC] #8842: Make sure msys2 builds non emulating binaries

[GHC]

#8842: Make sure msys2 builds non emulating binaries
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       Reporter:  schyler           |             Owner:
           Type:  task              |            Status:  new
       Priority:  normal            |         Milestone:
      Component:  Compiler          |           Version:  7.8.1-rc2
       Keywords:                    |  Operating System:  Windows
   Architecture:  Unknown/Multiple  |   Type of failure:  None/Unknown
     Difficulty:  Unknown           |         Test Case:
     Blocked By:                    |          Blocking:
Related Tickets:                    |
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 I came across this in my own project.

 MSys2 doesn't enter #ifdef blocks which test for _WIN32. Instead, it
 pretends to be Linux and has a set of headers which emulate things like
 mmap.

 These emulation functions are really really slow -- in my personal tests
 about 10x slower than calling the WINAPI -- so this ticket is just a
 reminder (it may already be done) for someone to check that MSys2 builds
 things non-emulated in GHC.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8842>
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