[GHC] #10735: Smooth out the differences between `compiler/utils/Pretty.hs` and `libraries/pretty`

[GHC]

#10735: Smooth out the differences between `compiler/utils/Pretty.hs` and
`libraries/pretty`
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        Reporter:  thomie            |                Owner:  (none)
            Type:  task              |               Status:  new
        Priority:  normal            |            Milestone:  8.0.1
       Component:  Compiler          |              Version:  7.0.1
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:  #1062, #1176,     |  Differential Rev(s):  Phab:D1130,
  #7666, #8809                       |  Phab:D1132
       Wiki Page:                    |
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Comment (by bgamari):

 Note that adinapoli has been doing some great work on this:
 https://github.com/haskell/pretty/pull/43.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10735#comment:27>
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