[MacPorts] #70326: gcc13, gcc14 build failures on arm64

[MacPorts]

#70326: gcc13, gcc14 build failures on arm64
---------------------------+---------------------------
  Reporter:  barracuda156  |      Owner:  (none)
      Type:  defect        |     Status:  new
  Priority:  Normal        |  Milestone:
 Component:  ports         |    Version:  2.9.3
Resolution:                |   Keywords:  arm64, sonoma
      Port:                |
---------------------------+---------------------------

Comment (by jmroot):

 It does seem to be missing a `unistd.h` include for the fallback case that
 uses dup2, but it should not be using that fallback because `F_GETFD`
 should definitely be defined in `fcntl.h`.

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Ticket URL: <https://trac.macports.org/ticket/70326#comment:4>
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