[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
---------------------------------+--------------------
  Reporter:  jhoyt4              |      Owner:  kencu
      Type:  defect              |     Status:  closed
  Priority:  Normal              |  Milestone:
 Component:  ports               |    Version:
Resolution:  fixed               |   Keywords:
      Port:  clang-9.0 clang-10  |
---------------------------------+--------------------

Comment (by thermalecology):

 So clang-9.0 builds but it's triggering build fails when trying to compile
 packages in R or when trying to compile scipy:

 clang: clang: error: error: invalid version number in '-mmacosx-version-
 min=11.0'

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Ticket URL: <https://trac.macports.org/ticket/61477#comment:42>
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