[MacPorts] #54198: upgrade: port:gcc7

[MacPorts]

#54198: upgrade: port:gcc7
---------------------+------------------------
  Reporter:  RJVB    |      Owner:  ryandesign
      Type:  update  |     Status:  accepted
  Priority:  Normal  |  Milestone:
 Component:  ports   |    Version:
Resolution:          |   Keywords:  haspatch
      Port:  gcc7    |
---------------------+------------------------

Comment (by raimue):

 What is the hold up here? Can we untangle the gcc7 upgrade to 7.1.0 from
 the additional libgcc/libc++ variants, if that is the problem?

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Ticket URL: <https://trac.macports.org/ticket/54198#comment:11>
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