[GHC] #12575: Support US spelling of `specialise` throughout

[GHC]

#12575: Support US spelling of `specialise` throughout
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           Reporter:  crockeea       |             Owner:
               Type:  bug            |            Status:  new
           Priority:  normal         |         Milestone:
          Component:  Compiler       |           Version:  8.0.1
           Keywords:                 |  Operating System:  Unknown/Multiple
       Architecture:                 |   Type of failure:  Other
  Unknown/Multiple                   |
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:
Differential Rev(s):                 |         Wiki Page:
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 GHC doesn't accept `-Wmissed-specializations`. Based on the
 [http://downloads.haskell.org/~ghc/latest/docs/html/users_guide/glasgow_exts.html
 #specialize-pragma docs], it seems like GHC is trying to support both
 spellings, so both spellings in the warning should be supported.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12575>
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