[MacPorts] #42742: update gmt to 4.5.12 and 5.1.1

[MacPorts]

#42742: update gmt to 4.5.12 and 5.1.1
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  Reporter:  florian@…      |      Owner:  macports-tickets@…
      Type:  update         |     Status:  new
  Priority:  Normal         |  Milestone:
 Component:  ports          |    Version:
Resolution:                 |   Keywords:  haspatch maintainer
      Port:  gmt gmt4 gmt5  |
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Comment (by ryandesign@…):

 Replying to [ticket:42742 florian@…]:
 > * gmt: introduce obsolete PortGroup

 Instead of this, I would like to delete the gmt port. We usually only keep
 stub "replaced_by" ports for a year, and gmt was replaced by gmt4 2.5
 years ago already.

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Ticket URL: <https://trac.macports.org/ticket/42742#comment:2>
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