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

[GHC]

#8894: Clean up `Coercible` plumbing
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        Reporter:  nomeata           |            Owner:
            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:
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Comment (by nomeata):

 Just gave it a shot, and indeed, the generated `libraries/ghc-prim/dist-
 install/doc/html/ghc-prim/GHC-Types.html#t:Coercible` shows `data
 Coercible a b` instead of `class Coercible a b`.

 GHCi gives the correct information upon `:browse GHC.Types`.

 Interestingly, `libraries/base/dist-install/doc/html/base/Data-
 Coerce.html` is correct. Since that is the official location for
 `Coercible`, I’ll actually push the change; this way someone who knows
 haddock can have a look (the changes affects three repositories, so having
 it as a branch is somewhat overkill).

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8894#comment:2>
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