[MacPorts] #59679: Unison 2.51.2_2 + aqua doesn't build on MacOS 10.13

[MacPorts]

#59679: Unison 2.51.2_2 + aqua doesn't build on MacOS 10.13
------------------------------+-----------------------------
  Reporter:  brunoomartin     |      Owner:  (none)
      Type:  defect           |     Status:  new
  Priority:  Normal           |  Milestone:
 Component:  ports            |    Version:  2.6.2
Resolution:                   |   Keywords:  unison 2.51.2_2
      Port:  unison 2.51.2_2  |
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Comment (by kencu):

 this port needs to indicate it requies a full xcode install, and use it.

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Ticket URL: <https://trac.macports.org/ticket/59679#comment:1>
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