[MacPorts] #67874: update mosquitto to 2.0.15

[MacPorts]

#67874: update mosquitto to 2.0.15
------------------------+----------------------
  Reporter:  danh1979   |      Owner:  slewsys
      Type:  update     |     Status:  assigned
  Priority:  Normal     |  Milestone:
 Component:  ports      |    Version:  2.8.1
Resolution:             |   Keywords:  haspatch
      Port:  mosquitto  |
------------------------+----------------------
Changes (by ryandesign):

 * owner:  (none) => slewsys
 * status:  new => assigned


Comment:

 `revision` should drop to `0` when the `version` is increased.

 http://mosquitto.org redirects to https://mosquitto.org so `master_sites`
 should be changed to `${homepage}/files/source/`.

 Needing to specify `-undefined dynamic_lookup` manually is surprising and
 suggests a bug in the build system. What error did you get before adding
 that? Did you file a bug report with upstream? Please provide its URL.

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Ticket URL: <https://trac.macports.org/ticket/67874#comment:1>
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