[GHC] #8742: Reuse scavenge_small_bitmap

[GHC]

#8742: Reuse scavenge_small_bitmap
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       Reporter:  Tarrasch          |             Owner:  simonmar
           Type:  task              |            Status:  new
       Priority:  lowest            |         Milestone:
      Component:  Runtime System    |           Version:  7.6.3
       Keywords:                    |  Operating System:  Unknown/Multiple
   Architecture:  Unknown/Multiple  |   Type of failure:  None/Unknown
     Difficulty:  Unknown           |         Test Case:
     Blocked By:                    |          Blocking:
Related Tickets:                    |
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 Hi, I've found that the `scavenge_small_bitmap` is in-lined at two places.
 I added this patch to remove code duplication.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8742>
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