[GHC] #9378: Make unknown LANGUAGE pragmas a warning, not an error

[GHC]

#9378: Make unknown LANGUAGE pragmas a warning, not an error
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              Reporter:  goldfire    |            Owner:
                  Type:  feature     |           Status:  new
  request                            |        Milestone:
              Priority:  normal      |          Version:  7.8.2
             Component:  Compiler    |         Keywords:
            Resolution:              |     Architecture:  Unknown/Multiple
      Operating System:              |       Difficulty:  Unknown
  Unknown/Multiple                   |       Blocked By:
       Type of failure:              |  Related Tickets:
  None/Unknown                       |
             Test Case:              |
              Blocking:              |
Differential Revisions:              |
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Changes (by thomie):

 * type:  bug => feature request


Comment:

 See the function `unsupportedExtnError` in the file
 `compiler/main/HeaderInfo.hs`.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9378#comment:6>
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