[GHC] #13444: Disable diagnostic coloring by default

[GHC]

#13444: Disable diagnostic coloring by default
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        Reporter:  hvr               |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  high              |            Milestone:  8.2.1
       Component:  Compiler          |              Version:  8.0.1
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Incorrect         |  Unknown/Multiple
  error/warning at compile-time      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by RyanGlScott):

 I do agree that the ability to configure the color scheme with a
 `GHC_COLORS` environment variable would be a cool feature. But I agree
 with David that I think outright disabling colors unless an environment
 variable is defined is going too far. Moreover, you can disable colors
 quite easily with `-fdiagnostics-color=never` in GHC, so I don't think
 this needs to be a release blocker.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13444#comment:4>
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