[GHC] #8894: Clean up `Coercible` plumbing

[GHC]

#8894: Clean up `Coercible` plumbing
-------------------------------------+------------------------------------
        Reporter:  nomeata           |            Owner:  nomeata
            Type:  task              |           Status:  new
        Priority:  normal            |        Milestone:
       Component:  Compiler          |          Version:  7.9
      Resolution:                    |         Keywords:
Operating System:  Unknown/Multiple  |     Architecture:  Unknown/Multiple
 Type of failure:  None/Unknown      |       Difficulty:  Unknown
       Test Case:                    |       Blocked By:
        Blocking:                    |  Related Tickets:  #8904
-------------------------------------+------------------------------------

Comment (by simonpj):

 I'm getting this:
 {{{
    typecheck/should_fail         TcCoercibleFail [stderr mismatch]
 (normal)
    typecheck/should_fail         TcCoercibleFail2 [stderr mismatch]
 (normal)
    typecheck/should_fail         TcCoercibleFail3 [stderr mismatch]
 (normal)
 }}}
 The error is
 {{{
 +TcCoercibleFail.hs:3:26:
 +    Module ‘GHC.Prim’ does not export ‘Coercible’
 }}}
 And indeed `GHC.Prim` doesn't export `Coercible` any more.  Did you
 validate?

 Simon

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8894#comment:10>
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