[GHC] #11757: Turn on (and require) C99/C11 mode by default

[GHC]

#11757: Turn on (and require) C99/C11 mode by default
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        Reporter:  hvr               |                Owner:
            Type:  task              |               Status:  new
        Priority:  normal            |            Milestone:  8.2.1
       Component:  Build System      |              Version:
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by hvr):

 be2a7baf15c6cf414e2287bff3ed345c50de88bd / phab:D2056 (reference added
 manually due to missing Trac ticket reference in commit msg)

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11757#comment:4>
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