[MacPorts] #50671: boost: Update to 1.64.0

[MacPorts]

#50671: boost: Update to 1.64.0
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  Reporter:  eborisch  |      Owner:  ryandesign
      Type:  update    |     Status:  new
  Priority:  Normal    |  Milestone:
 Component:  ports     |    Version:  2.3.4
Resolution:            |   Keywords:  haspatch
      Port:  boost     |
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Comment (by gaming-hacker):

 why doesn't macports create it's own github fork of boost?  apply patches,
 clean it up, etc. create a custom build bot and let the bot thrash the
 updates.

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Ticket URL: <https://trac.macports.org/ticket/50671#comment:36>
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