[GHC] #13392: ghc --show-options lists flags twice

[GHC]

#13392: ghc --show-options lists flags twice
--------------------------------------+---------------------------------
           Reporter:  ThreeFx         |             Owner:  (none)
               Type:  bug             |            Status:  new
           Priority:  low             |         Milestone:  ⊥
          Component:  Compiler        |           Version:  8.0.1
           Keywords:  newcomer        |  Operating System:  Linux
       Architecture:  x86_64 (amd64)  |   Type of failure:  None/Unknown
          Test Case:                  |        Blocked By:
           Blocking:                  |   Related Tickets:
Differential Rev(s):                  |         Wiki Page:
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 Running `ghc --show-options` with GHC version 8.0.1 returns the flags `-O`
 and `-W` twice.

 To check this, execute the following command in your shell:

 {{{
 ghc --show-options | sort | uniq -d
 }}}

 At commit `669333d8afaf388a3ce4a56e383b24ea2bdea145` (GHC 8.1.20170304)
 only `-O` is duplicated.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13392>
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