[MacPorts] #59834: Boost: update to 1.74.0

[MacPorts]

#59834: Boost: update to 1.74.0
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  Reporter:  michaelld  |      Owner:  (none)
      Type:  update     |     Status:  new
  Priority:  Normal     |  Milestone:
 Component:  ports      |    Version:
Resolution:             |   Keywords:
      Port:  boost      |
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Comment (by michaelld):

 Yes that's still my hope ... not sure when I'll get to this, but it would
 be good to get it done! The first step would be to create the `boost171`
 port & move all current ports to use it instead of `boost`. Then we could
 start adding in `boostXYZ` & `boost` (latest release) ports, which would
 be standalone & we could then update any port that depends on Boost to
 whatever `boostXYZ` it works with. Eventually we'd want to deprecate older
 `boostXYZ`. This will be a bit of a pain to maintain for older OSX /
 macOS, but it provides the most robust solution that allows us to easily
 update `boost` for development purposes.

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Ticket URL: <https://trac.macports.org/ticket/59834#comment:13>
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