[MacPorts] #52776: clang build fails due to __SWIFT_UNAVAILABLE_MSG used in the SDK but not defined for some reason

[MacPorts]

#52776: clang build fails due to __SWIFT_UNAVAILABLE_MSG used in the SDK but not
defined for some reason
------------------------+----------------------
  Reporter:  murrayE    |      Owner:  jeremyhu
      Type:  defect     |     Status:  assigned
  Priority:  Normal     |  Milestone:
 Component:  ports      |    Version:  2.3.4
Resolution:             |   Keywords:
      Port:  clang-3.8  |
------------------------+----------------------

Comment (by ken-cunningham-webuse):

 I believe this issue could relate to a rogue
 {{{
  /opt/local/include/Availability.h
 }}}
 as per  the mailing list discussion. If that is proven to be so, it could
 be closed.

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Ticket URL: <https://trac.macports.org/ticket/52776#comment:5>
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