[MacPorts] #54504: xorg-server 1.18.4_2: fails to compile on sierra

[MacPorts]

#54504: xorg-server 1.18.4_2: fails to compile on sierra
--------------------------+----------------------
  Reporter:  EdHarry      |      Owner:  jeremyhu
      Type:  defect       |     Status:  assigned
  Priority:  Normal       |  Milestone:
 Component:  ports        |    Version:  2.4.1
Resolution:               |   Keywords:  sierra
      Port:  xorg-server  |
--------------------------+----------------------

Comment (by jeremyhu):

 I thought I blocked clang-3.7 on Sierra because of this:

 {{{
 :info:build
 /System/Library/Frameworks/Foundation.framework/Headers/NSObject.h:44:12:
 error: unknown property attribute 'class'
 :info:build @property (class, readonly) BOOL supportsSecureCoding;
 :info:build            ^
 }}}

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Ticket URL: <https://trac.macports.org/ticket/54504#comment:9>
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