[MacPorts] #53758: gcc6 @6.3.0_2: g++ fails to find stdc++ includes when -isysroot set

[MacPorts]

#53758: gcc6 @6.3.0_2: g++ fails to find stdc++ includes when -isysroot set
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  Reporter:  ibethune  |      Owner:
      Type:  defect    |     Status:  new
  Priority:  Normal    |  Milestone:
 Component:  ports     |    Version:  2.4.0
Resolution:            |   Keywords:
      Port:  gcc6      |
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Comment (by kencu):

 Look at [ticket:53726]

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Ticket URL: <https://trac.macports.org/ticket/53758#comment:1>
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