[GHC] #10150: Suppress orphan instance warning per instance

[GHC]

#10150: Suppress orphan instance warning per instance
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              Reporter:  ezyang      |             Owner:
                  Type:  feature     |            Status:  new
  request                            |         Milestone:
              Priority:  low         |           Version:  7.11
             Component:  Compiler    |  Operating System:  Unknown/Multiple
  (Type checker)                     |   Type of failure:  None/Unknown
              Keywords:              |        Blocked By:
          Architecture:              |   Related Tickets:
  Unknown/Multiple                   |
             Test Case:              |
              Blocking:              |
Differential Revisions:              |
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 In the same way we have overlapping/incoherent instance pragmas which can
 be applied on a per instance basis, it would be good to have a `-fno-warn-
 orphan-instance` pragma which can be applied on a per-instance basis.

 Annoyingly, there is not an obvious syntax to use for this case, since SOP
 for a module with orphan instances is `{-# GHC_OPTIONS -fno-warn-orphans
 #-}`

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10150>
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