[MacPorts] #57117: upgrade last users of protobuf-cpp to protobuf3-cpp

[MacPorts]

#57117: upgrade last users of protobuf-cpp to protobuf3-cpp
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  Reporter:  pmetzger                            |      Owner:  (none)
      Type:  enhancement                         |     Status:  new
  Priority:  Normal                              |  Milestone:
 Component:  ports                               |    Version:
Resolution:                                      |   Keywords:
      Port:  caffe MyPaint opencv raceintospace  |
  shogun-devel sumo                              |
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Comment (by kencu):

 Replying to [comment:8 ryandesign]:
 > My point was: isn't it protobuf3-cpp's responsibility, not the
 responsibility of caffe or the caffe portfile or of any other software
 that uses protobuf3-cpp, to specify the `-std=c++11` flag? If we fix this
 at one central place, in protobuf3-cpp, isn't that a simple fix?

 Ah, I get you now. Turns out, no. The port that is **using** protobuf3-cpp
 has to now be built with `-std=c++11` so it can properly process the
 protobuf 3.6.1+ headers.

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Ticket URL: <https://trac.macports.org/ticket/57117#comment:10>
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