[MacPorts] #46527: ld64 @97.17_4: error: Availability.h: No such file or directory

[MacPorts]

#46527: ld64 @97.17_4: error: Availability.h: No such file or directory
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  Reporter:  ryandesign@…       |      Owner:  jeremyhu@…
      Type:  defect             |     Status:  new
  Priority:  Normal             |  Milestone:
 Component:  ports              |    Version:  2.3.3
Resolution:                     |   Keywords:
      Port:  libunwind-headers  |
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Comment (by ryandesign@…):

 That bug was opened October 2013, though I see there was some activity
 from you today. Do we think this is an easy problem to fix soon? As it
 stands, no ports can be built on Tiger, since all ports on Tiger depend on
 apple-gcc42 which depends on the now unbuildable ld64.

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Ticket URL: <https://trac.macports.org/ticket/46527#comment:2>
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