[GHC] #8944: Warn instead of stopping on misplaced Haddock comments

[GHC]

#8944: Warn instead of stopping on misplaced Haddock comments
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              Reporter:  Fuuzetsu    |            Owner:
                  Type:  feature     |           Status:  new
  request                            |        Milestone:
              Priority:  normal      |          Version:  7.9
             Component:  Compiler    |         Keywords:
  (Parser)                           |     Architecture:  Unknown/Multiple
            Resolution:              |       Difficulty:  Unknown
      Operating System:              |       Blocked By:
  Unknown/Multiple                   |  Related Tickets:
       Type of failure:              |
  None/Unknown                       |
             Test Case:              |
              Blocking:              |
Differential Revisions:  Phab:D452   |
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Comment (by goldfire):

 I think this should be enabled with `-Wall`, even if `haddock` is not
 enabled. That way, when I'm developing, but before trying to release and
 build docs, I can learn about bad Haddock comments.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8944#comment:4>
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