[GHC] #14508: Bring up Appveyor for Windows CI

[GHC]

#14508: Bring up Appveyor for Windows CI
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        Reporter:  bgamari           |                Owner:  bgamari
            Type:  task              |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Continuous        |              Version:  8.2.1
  Integration                        |
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by bgamari):

 Several members of the newly formed GHC Devops Committee argued strongly
 against Jenkins. Their arguments are summarized on
 wiki:ContinuousIntegration

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14508#comment:4>
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