[MacPorts] #60148: mkvtoolnix: Update to version 43

[MacPorts]

#60148: mkvtoolnix: Update to version 43
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  Reporter:  mf2k        |      Owner:  ryandesign
      Type:  update      |     Status:  assigned
  Priority:  Normal      |  Milestone:
 Component:  ports       |    Version:
Resolution:              |   Keywords:
      Port:  mkvtoolnix  |
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Comment (by ryandesign):

 When I tried to update to 42 or newer, it would not compile on High Sierra
 anymore. Since that is still a recent OS, I would like to have the port
 continue to use the old version on High Sierra and older. (Or, if you know
 how to fix the build failure on High Sierra, that would be even better.)

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Ticket URL: <https://trac.macports.org/ticket/60148#comment:1>
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