[GHC] #10752: Print which warning-flag controls/enabled an emitted warning

[GHC]

#10752: Print which warning-flag controls/enabled an emitted warning
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        Reporter:  hvr               |                Owner:  barrucadu
            Type:  feature request   |               Status:  merge
        Priority:  normal            |            Milestone:  8.0.1
       Component:  Compiler          |              Version:
      Resolution:  fixed             |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Incorrect         |  Unknown/Multiple
  warning at compile-time            |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):  Phab:D1943
       Wiki Page:  Design/Warnings   |
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Changes (by bgamari):

 * status:  closed => merge


Comment:

 This introduced a small bug which is fixed by Phab:D2077. This will need
 merging.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10752#comment:24>
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