[GHC] #12991: panic when using IrredPreds in a type checker plugin.

[GHC]

#12991: panic when using IrredPreds in a type checker plugin.
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        Reporter:  owen              |                Owner:
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.0.1
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Compile-time      |  Unknown/Multiple
  crash or panic                     |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Changes (by owen):

 * Attachment "ghc-plugin-test.tgz" added.

 tcplugin and test case

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12991>
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