[MacPorts] #54949: gcc5 @5.4.0_2 fails to build on macOS 10.13

[MacPorts]

#54949: gcc5 @5.4.0_2 fails to build on macOS 10.13
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  Reporter:  matteopuel  |      Owner:
      Type:  defect      |     Status:  new
  Priority:  Normal      |  Milestone:
 Component:  ports       |    Version:
Resolution:              |   Keywords:  highsierra
      Port:  gcc5        |
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Comment (by kencu):

 Replying to [comment:13 ryandesign]:
 > Ken, is there a specific reason why this patch is not safe to apply for
 all versions of Xcode?
 I suspect it probably could apply to all versions, but it seemed like it
 might take a week to build them all to find out ;> I thought I'd fix the
 broken versions, leave the known working ones alone, and then we'd update
 gcc5 to 5.5.0 soonish and run the gauntlet with all mac versions then.

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Ticket URL: <https://trac.macports.org/ticket/54949#comment:14>
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