[GHC] #15342: Mark -XAutoDeriveTypeable as deprecated

[GHC]

#15342: Mark -XAutoDeriveTypeable as deprecated
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           Reporter:  monoidal       |             Owner:  (none)
               Type:  bug            |            Status:  new
           Priority:  normal         |         Milestone:  8.6.1
          Component:  Compiler       |           Version:  8.4.3
           Keywords:                 |  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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 The language extension `-XAutoDeriveTypeable` is not needed since #9858.

 It was earlier marked as redundant in GHC documentation. I propose that
 GHC gives a clear deprecation message.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15342>
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