[GHC] #657: add WARNING pragma

[GHC]

#657: add WARNING pragma
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  Reporter:  ijones       |          Owner:         
      Type:  task         |         Status:  new    
  Priority:  normal       |      Milestone:         
 Component:  Compiler     |        Version:  6.4.1  
  Severity:  normal       |     Resolution:         
  Keywords:               |             Os:  Unknown
Difficulty:  Easy (1 hr)  |   Architecture:  Unknown
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Comment (by simonpj):

 This could be easily done if we can agree about what we want.

 Should "WARNING" be "WARN_USE" or "WARN_USE_OF" or "WARN_AT_USE" or
 something like that?  Something more self explanatory.

 (Or use hyphens?  "WARN-USE" or "WARN-USE-OF" etc.)

 Then DEPRECATED becomes "WARN-USE" with an automatic prefix "x is
 deprecated.".  Right?

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Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/657>
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