[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:11 ryandesign]:
 > I'm suggesting putting the flag in protobuf.pc (and protobuf-lite.pc if
 applicable).
 At first glance, I can see the logic in that. However, what if the port
 using protobuf actually needs `-std=c++14` or some newer standard than
 that? Then that flag from protobuf would mess things up...

 I looked in my pkgconfig directory, and found that only `icu` passed in a
 `-std=c++N` flag out of all the *.pc files in there.

 In addition, it seems that pkg-config is not currently set up to (easily)
 pass CXXFLAGS <https://stackoverflow.com/questions/46550299/why-doesnt-
 pkg-config-support-cxxflags>...

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Ticket URL: <https://trac.macports.org/ticket/57117#comment:13>
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