[MacPorts] #56433: update gmt4 to 4.5.17

[MacPorts]

#56433: update gmt4 to 4.5.17
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  Reporter:  fvaccari  |      Owner:  tenomoto
      Type:  update    |     Status:  assigned
  Priority:  Normal    |  Milestone:
 Component:  ports     |    Version:
Resolution:            |   Keywords:
      Port:  gmt4      |
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Comment (by fvaccari):

 Wasn't aware of the pull request way. Spent half a day to make a proper
 one, hope didn't make too many formal mistakes...

 [https://github.com/fvaccari/macports-ports/pull/1]

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Ticket URL: <https://trac.macports.org/ticket/56433#comment:3>
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