[MacPorts] #56294: boost: update to 1.70.0 (was: boost: update to 1.69.0)

[MacPorts]

#56294: boost: update to 1.70.0
------------------------+---------------------------------
  Reporter:  michaelld  |      Owner:  ryandesign
      Type:  update     |     Status:  assigned
  Priority:  Normal     |  Milestone:
 Component:  ports      |    Version:
Resolution:             |   Keywords:  haspatch maintainer
      Port:  boost      |
------------------------+---------------------------------
Description changed by michaelld:

Old description:

> Boost 1.69.0 is out as of 12/12/2018.
>
> Because the Portfile currently uses "--layout=tagged", the resulting
> libraries names change from the Boost 1.68.0 to include an abbreviated
> architecture (e.g., "x64" for Intel 64-bit; "p32" for PPC 32-bit); thus
> for example, the prior naming might be "libboost_system-mt.dylib", while
> the new naming is "libbboost_system-mt-x64.dylib". This slight change
> combined with a defect in how CMake works with Clang results in the
> FindBoost.cmake script failing to detect the new library names with
> significant coercion.
>
> This issue is resolved by moving to "--layout=system", which reverts the
> library names to just the minimum for each component; for example here
> "libboost_system.dylib".
>
> Most of the changes to this latest Boost itself seem to be compatible
> with the ports I've tried building with it, once the Portfile is fixed to
> properly detect the changed name. That said, the 10 or so ports I checked
> pale compared with the total number of ports that depend on Boost (some
> 250 in total).
>
> Verifying that "enough" of these ports build and function properly
> "enough" is an arduous task. We in MacPorts have yet to determine a
> reasonable approach to updating Boost, so the version provided in
> MacPorts regularly lags the latest release. Please be patient.

New description:

 Boost 1.70.0 is out as of 20190412.

 Prior Description, which is all likely still relevant:
 [[
 Boost 1.69.0 is out as of 120181212.

 Because the Portfile currently uses "--layout=tagged", the resulting
 libraries names change from the Boost 1.68.0 to include an abbreviated
 architecture (e.g., "x64" for Intel 64-bit; "p32" for PPC 32-bit); thus
 for example, the prior naming might be "libboost_system-mt.dylib", while
 the new naming is "libbboost_system-mt-x64.dylib". This slight change
 combined with a defect in how CMake works with Clang results in the
 FindBoost.cmake script failing to detect the new library names with
 significant coercion.

 This issue is resolved by moving to "--layout=system", which reverts the
 library names to just the minimum for each component; for example here
 "libboost_system.dylib".

 Most of the changes to this latest Boost itself seem to be compatible with
 the ports I've tried building with it, once the Portfile is fixed to
 properly detect the changed name. That said, the 10 or so ports I checked
 pale compared with the total number of ports that depend on Boost (some
 250 in total).

 Verifying that "enough" of these ports build and function properly
 "enough" is an arduous task. We in MacPorts have yet to determine a
 reasonable approach to updating Boost, so the version provided in MacPorts
 regularly lags the latest release. Please be patient.
 ]]

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Ticket URL: <https://trac.macports.org/ticket/56294#comment:19>
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