[MacPorts] #61477: clang-9.0 fails to build on Big Sur macOS 11.0.1 Xcode 12.2

[MacPorts]

#61477: clang-9.0 fails to build on Big Sur macOS 11.0.1 Xcode 12.2
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  Reporter:  jhoyt4     |      Owner:  kencu
      Type:  defect     |     Status:  assigned
  Priority:  Normal     |  Milestone:
 Component:  ports      |    Version:
Resolution:             |   Keywords:
      Port:  clang-9.0  |
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Changes (by jhoyt4):

 * Attachment "main.clang10.log" added.

 clang10 output

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Ticket URL: <https://trac.macports.org/ticket/61477>
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