[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:  macports-tickets@…
     Type:  defect          |     Status:  new
 Priority:  Normal          |  Milestone:
Component:  ports           |    Version:  2.3.4
 Keywords:  sierra          |       Port:  org-libX11
----------------------------+--------------------------------
 Configure script fails with error:

 {{{
 :info:configure checking for cpp... /usr/bin/cpp
 :info:configure checking if /usr/bin/cpp requires -undef... configure:
 error: /usr/bin/cpp defines unix with or without -undef.  I don't know
 what to do.
 :info:configure Command failed:  cd
 "/opt/local/var/macports/build/_opt_local_var_macports_sources_rsync.macports
 .org_release_tarballs_ports_x11_xorg-libX11/xorg-libX11/work/libX11-1.6.3"
 && ./configure --prefix=/opt/local --without-xmlto --without-fop
 --disable-specs
 :info:configure Exit code: 1
 }}}

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