[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 michaelld):

 Agreed, Chris. I'll do a WIP PR hopefully later today.

 Updates from the past week, mostly discussing the new Boost 1.70.0 with
 others who have also been trying it out:

 Disable the new CMake build scripts provided by Boost, as they are not yet
 ready for prime time; just use the one provided by CMake as it should work
 as currently expected by other ports. I'll post that portfile tweak once
 I've confirmed it, per ...

 I'm updating Boost on my 10.14 build system today & will start testing
 dependent ports as the week goes on, hopefully creating something of an
 automated script to do so. Others can also test dependent ports. Once we
 hit a reasonable threshold (80%? 90%?) of them being functional, I'd be
 ready to commit & work on fixing up the remainder afterwards.

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Ticket URL: <https://trac.macports.org/ticket/56294#comment:26>
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