[MacPorts] #65415: libgcc9 @9.5.0_1: builds fail on 10.8, 10.9, 10.10

[MacPorts]

#65415: libgcc9 @9.5.0_1: builds fail on 10.8, 10.9, 10.10
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  Reporter:  chillin-  |      Owner:  i0ntempest
      Type:  defect    |     Status:  assigned
  Priority:  Normal    |  Milestone:
 Component:  ports     |    Version:  2.7.2
Resolution:            |   Keywords:
      Port:  libgcc9   |
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Comment (by cjones051073):

 So, it appears all the failing platforms are using MP clan 14 to build,
 whereas 10.11, the oldest to be ok is not. Perhaps its enough to blacklist
 this compiler (and perhaps 13,12…) so fallback to a older one.
 Unfortunately the logs for the last builds to work on these platforms are
 not available to check what worked so its going to be a bit of trial and
 error…

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Ticket URL: <https://trac.macports.org/ticket/65415#comment:9>
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