[MacPorts] #58856: Boost: update to 1.71.0

[MacPorts]

#58856: Boost: update to 1.71.0
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  Reporter:  michaelld    |      Owner:  michaelld
      Type:  enhancement  |     Status:  assigned
  Priority:  Normal       |  Milestone:
 Component:  ports        |    Version:
Resolution:               |   Keywords:
      Port:  boost        |
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Comment (by michaelld):

 https://github.com/macports/macports-ports/pull/5086

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Ticket URL: <https://trac.macports.org/ticket/58856#comment:2>
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