[MacPorts] #47553: compilers portgroup: add option for gcc5

[MacPorts]

#47553: compilers portgroup: add option for gcc5
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  Reporter:  ryandesign@…  |      Owner:  sean@…
      Type:  enhancement   |     Status:  new
  Priority:  Normal        |  Milestone:
 Component:  ports         |    Version:
Resolution:                |   Keywords:
      Port:  compilers     |
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Comment (by ryandesign@…):

 Also, please add clang 3.6.

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Ticket URL: <https://trac.macports.org/ticket/47553#comment:1>
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