[MacPorts] #52335: xorg-libX11 @1.6.3: fails to configure on sierra with Xcode 8.0

[MacPorts]

#52335: xorg-libX11 @1.6.3: fails to configure on sierra with Xcode 8.0
-----------------------------+------------------------
  Reporter:  Julian.Byrne@…  |      Owner:  jeremyhu@…
      Type:  defect          |     Status:  new
  Priority:  Normal          |  Milestone:
 Component:  ports           |    Version:  2.3.4
Resolution:                  |   Keywords:  sierra
      Port:  xorg-libX11     |
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Comment (by Julian.Byrne@…):

 Whoops. I aliased /opt/local/bin/xcrun to /usr/bin/true as part of a
 workaround #52200. That's the reason for the noop - sorry for the
 confusion.

 {{{
 /usr/bin/cpp -dM -undef - - < /dev/null|grep unix
 /usr/bin/cpp -dM - - < /dev/null|grep unix
 }}}

 both give nothing - the reason for the failure of the configure script
 which depends on the "unix" definition for it's check.

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Ticket URL: <https://trac.macports.org/ticket/52335#comment:4>
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