[MacPorts] #69173: port fails to upgrade to 2.9.0

[MacPorts]

#69173: port fails to upgrade to 2.9.0
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  Reporter:  mouse07410  |      Owner:  (none)
      Type:  defect      |     Status:  new
  Priority:  Normal      |  Milestone:
 Component:  base        |    Version:  2.9.0
Resolution:              |   Keywords:
      Port:              |
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Comment (by mouse07410):

 @kencu, it's  {{{port}}} itself that's trying to outsmart {{{xcrun}}} (in
 this ticket's case, during attempt to rebuild itself from source). I
 merely created a (hopefully, minimal) reproducer of the problem.

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Ticket URL: <https://trac.macports.org/ticket/69173#comment:6>
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