[MacPorts] #71592: qt5-qtbase @ 5.11.3_12 -- Failed to Configure "error: invalid value 'c++17' in '-std=c++17"

[MacPorts]

#71592: qt5-qtbase @ 5.11.3_12 -- Failed to Configure "error: invalid value 'c++17'
in '-std=c++17"
-----------------------+------------------------
 Reporter:  RobK88     |      Owner:  (none)
     Type:  defect     |     Status:  new
 Priority:  Normal     |  Milestone:
Component:  ports      |    Version:  2.10.5
 Keywords:  elcapitan  |       Port:  qt5-qtbase
-----------------------+------------------------
 I am unable to upgrade `qt511-qtbase` to @ 5.11.3_12 on El Capitan. The
 port fails to configure.

 `error: invalid value 'c++17' in '-std=c++17`

 See attached configure.log

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Ticket URL: <https://trac.macports.org/ticket/71592>
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