[GHC] #11128: New `-fwarn-noncanonical-monad-instances` warning

[GHC]

#11128: New `-fwarn-noncanonical-monad-instances` warning
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           Reporter:  hvr            |             Owner:  hvr
               Type:  feature        |            Status:  new
  request                            |
           Priority:  normal         |         Milestone:  8.0.1
          Component:  Compiler       |           Version:  7.10.2
           Keywords:                 |  Operating System:  Unknown/Multiple
       Architecture:                 |   Type of failure:  None/Unknown
  Unknown/Multiple                   |
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:
Differential Rev(s):                 |         Wiki Page:
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 placeholder -- I needed a ticket number; will flesh out description asap

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11128>
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