[GHC] #7305: T5975a is broken on Windows

[GHC]

#7305: T5975a is broken on Windows
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        Reporter:  simonmar          |            Owner:
            Type:  bug               |           Status:  new
        Priority:  normal            |        Milestone:  7.8.1
       Component:  Test Suite        |          Version:  7.6.1
      Resolution:                    |         Keywords:
Operating System:  Unknown/Multiple  |     Architecture:  Unknown/Multiple
 Type of failure:  None/Unknown      |       Difficulty:  Unknown
       Test Case:                    |       Blocked By:
        Blocking:                    |  Related Tickets:
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Comment (by ezyang):

 It appears that it is not sufficient to just convert the pre_cmd/post_cmd
 to accept a Unicode string, as this breaks when using `os.system`, because
 Python attempts to transcode to ASCII. So we should convert everything to
 use subprocess/spawnv instead (both of which support Unicode), probably by
 manually invoking the shell we want.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/7305#comment:3>
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