[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
      Resolution:                    |             Keywords:  newcomer
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  Other             |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by tmcgilchrist):

 I'd like to have a go at fixing this issue.

 Just so I understand it correctly a fix for this would involve supporting
 both `specialisation` spelling for that command line argument.
 I believe I have something working for `-Wmissed-specializations` and
 `-Wall-missed-specializations`.

 I couldn't find any specific tests that cover these command line
 arguments, is there any?

 As a follow up, I'm not sure if it's required, but there are other flags
 that appear to have the UK spelling of `specialise` like `specialise-
 aggressively` and `cross-module-specialise`

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12575#comment:2>
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