[MacPorts] #56294: boost: update to 1.70.0

[MacPorts]

#56294: boost: update to 1.70.0
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  Reporter:  michaelld  |      Owner:  ryandesign
      Type:  update     |     Status:  assigned
  Priority:  Normal     |  Milestone:
 Component:  ports      |    Version:
Resolution:             |   Keywords:  haspatch maintainer
      Port:  boost      |
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Comment (by blair):

 I started working on a PR for the boost package. Two of the patches needed
 work, you can find them in my local branch: https://github.com/blair
 /macports-ports/tree/boost-1.70.0 .

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Ticket URL: <https://trac.macports.org/ticket/56294#comment:34>
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