[GHC] #9713: Update comment about C helper for dynamic exports.

[GHC]

#9713: Update comment about C helper for dynamic exports.
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              Reporter:  int-e       |            Owner:
                  Type:  task        |           Status:  patch
              Priority:  normal      |        Milestone:
             Component:  Compiler    |          Version:  7.8.3
            Resolution:              |         Keywords:
      Operating System:              |     Architecture:  Unknown/Multiple
  Unknown/Multiple                   |       Difficulty:  Easy (less than 1
       Type of failure:  Other       |  hour)
             Test Case:              |       Blocked By:
              Blocking:              |  Related Tickets:
Differential Revisions:              |
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Comment (by int-e):

 In fact there were two relevant API changes,
 03a9ff01812afc81eb5236fd3063cbec44cf469e and
 8b75acd3ca25165536f18976c8d80cb62ad613e4.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9713#comment:4>
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