[MacPorts] #47578: mkvtoolnix: upgrade to 7.8.0

[MacPorts]

#47578: mkvtoolnix: upgrade to 7.8.0
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  Reporter:  mojca@…     |      Owner:  macports-tickets@…
      Type:  update      |     Status:  new
  Priority:  Normal      |  Milestone:
 Component:  ports       |    Version:
Resolution:              |   Keywords:
      Port:  mkvtoolnix  |
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Comment (by ryandesign@…):

 Here is the [https://github.com/mbunkus/mkvtoolnix/issues/1172 upstream
 bug report] and the rather larger than expected
 [https://github.com/mbunkus/mkvtoolnix/commit/df0df0f83b2dceb390945c9393621f1c11c466d0
 commit that fixed it] in which they (surprisingly!) decided to include a
 copy of the old utf8_codecvt_facet.hpp in the mkvtoolnix codebase rather
 than adapt to the new way.

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Ticket URL: <https://trac.macports.org/ticket/47578#comment:3>
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