[MacPorts] #59323: jtc @1.7.4: error: invalid value 'c++14' in '-std=c++14'

[MacPorts]

#59323: jtc @1.7.4: error: invalid value 'c++14' in '-std=c++14'
-------------------------+-------------------------
  Reporter:  ryandesign  |      Owner:  herbygillot
      Type:  defect      |     Status:  assigned
  Priority:  Normal      |  Milestone:
 Component:  ports       |    Version:  2.6.1
Resolution:              |   Keywords:
      Port:  jtc         |
-------------------------+-------------------------

Comment (by ryandesign):

 [https://build.macports.org/builders/ports-10.9_x86_64-builder/builds/101835/steps
 /install-port/logs/stdio Here is the latest build log] which does indeed
 show the same failure. It still shows /usr/bin/clang++ being used. The log
 does not mention anything about blacklisting. I am not familiar with how
 the new `compiler.cxx_standard` option works so I cannot offer any
 suggestions for debugging this.

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Ticket URL: <https://trac.macports.org/ticket/59323#comment:3>
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