[MacPorts] #58199: cmake: build failure on OSX 10.11 due to LegacySupport PortGroup

[MacPorts]

#58199: cmake: build failure on OSX 10.11 due to LegacySupport PortGroup
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  Reporter:  dbl001  |      Owner:  michaelld
      Type:  defect  |     Status:  assigned
  Priority:  Normal  |  Milestone:
 Component:  ports   |    Version:  2.5.4
Resolution:          |   Keywords:
      Port:  cmake   |
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Comment (by cjones051073):

 In my opinion, from MacPorts the advice should be if you are running
 OSX10.11, to stick with Xcode 7. Xcode 8 does not have the 10.11 SDK, only
 10.12, which is the trigger for all the issues here.

 That is not to say we should find a way to work around this, if we can.
 Just the advice should be to avoid it in the first place ;)

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Ticket URL: <https://trac.macports.org/ticket/58199#comment:27>
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