[MacPorts] #60080: qt513-qtwebengine fails building (on MacOS 10.12)

[MacPorts]

#60080: qt513-qtwebengine fails building (on MacOS 10.12)
------------------------------+---------------------------------
  Reporter:  Greisby          |      Owner:  MarcusCalhoun-Lopez
      Type:  defect           |     Status:  assigned
  Priority:  Normal           |  Milestone:
 Component:  ports            |    Version:
Resolution:                   |   Keywords:
      Port:  qt5-qtwebengine  |
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Comment (by MarcusCalhoun-Lopez):

 According to the log, you are using Xcode 8.3.3.\\
 `__builtin_available` seems to have been [https://lists.qt-
 project.org/pipermail/development/2017-September/030879.html introduced in
 Xcode 9].\\
 I need to upgrade the Portfile to fail more gracefully, but that does not
 help you.\\
 Is there any way for you to upgrade to Xcode 9?

 Another possibility is to **not** use the `+examples` variant.\\
 That should allow you to install the
 [http://packages.macports.org/qt513-qtwebengine/ binary version] of
 qt513-qtwebengine.

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Ticket URL: <https://trac.macports.org/ticket/60080#comment:4>
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