[GHC] #2968: add test for C trigraphs

[GHC]

#2968: add test for C trigraphs
---------------------------+------------------------------------------------
  Reporter:  duncan        |          Owner:                  
      Type:  task          |         Status:  new             
  Priority:  normal        |      Milestone:  6.12 branch     
 Component:  Compiler      |        Version:  6.10.1          
Resolution:                |       Keywords:                  
Difficulty:  Unknown       |             Os:  Unknown/Multiple
  Testcase:                |   Architecture:  Unknown/Multiple
   Failure:  None/Unknown  |  
---------------------------+------------------------------------------------
Changes (by igloo):

  * failure:  => None/Unknown
  * milestone:  6.12.1 => 6.12 branch

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Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/2968#comment:6>
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