[GHC] #11454: Do not suggest deprecated flags

[GHC]

#11454: Do not suggest deprecated flags
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           Reporter:  thomie         |             Owner:
               Type:  task           |            Status:  new
           Priority:  normal         |         Milestone:
          Component:  Compiler       |           Version:  7.10.3
           Keywords:  newcomer       |  Operating System:  Unknown/Multiple
       Architecture:                 |   Type of failure:  None/Unknown
  Unknown/Multiple                   |
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:
Differential Rev(s):                 |         Wiki Page:
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 When you misspell the name of a flag, GHC outputs a nice list of similar
 flags that do exist:
 {{{
 $ ghc-8.0.1 -W-redundant-constraints
 ghc: unrecognised flag: -W-redundant-constraints
 did you mean one of:
   -Wredundant-constraints
   -Wno-redundant-constraints
   -fwarn-redundant-constraints
 }}}

 But since the `-fwarn` flags are deprecated, they should not be suggested.
 Neither should any of the other deprecated flags.

 For a newcomer: the code is `compiler/main/DynFlags.hs`.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11454>
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