[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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Changes (by hvr):

 * cc: kgardas (added)


Comment:

 related change regarding `_XOPEN_SOURCE`/`_POSIX_C_SOURCE`:
 91b96e1ccce6a642d710ce40211e1795d01abf04 and phab:D2053

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11757#comment:3>
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