[MacPorts] #48471: FSF gcc48 fails to compile projects on El Capitan due to OS X SDK bug in Availability.h

[MacPorts]

#48471: FSF gcc48 fails to compile projects on El Capitan due to OS X SDK bug in
Availability.h
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  Reporter:  jasonw@…  |      Owner:  mww@…
      Type:  defect    |     Status:  new
  Priority:  Normal    |  Milestone:
 Component:  ports     |    Version:  2.3.3
Resolution:            |   Keywords:  elcapitan
      Port:  gcc48     |
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Comment (by murrayeisenberg@…):

 Replying to [comment:41 jeremyhu@…]:
 > Yes.  If you want, you can just manually edit Availability.h to replace
 the '`defined(__has_feature)`' with '`defined(__has_attribute)`' for the
 OSX and iOS availability macros, but you do so at your own risk because
 you know what you're doing ;)

 Even using {{{sudo}}} with an admin account on OS X 10.11.1 did not allow
 me to edit Availability.h. How did you do it (if you did)?

 Also, I could not even build gcc48, again apparently due to the same issue
 with Availability.h.

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Ticket URL: <https://trac.macports.org/ticket/48471#comment:48>
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