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

[MacPorts]

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

Comment (by kencu):

 for some of these, switching to protobuf3-cpp and then just forcing the
 build to clang-7.0 (or newer) might be the easiest way out.

 clang-7.0 defaults to a newer c++ standard, so you don't need to monkey
 around with the build system, for example, `caffe` [ticket:57093].

 Naturally, fix it all up if you want, but it's pretty simple to just
 switch up the compiler and you're done...

-- 
Ticket URL: <https://trac.macports.org/ticket/57117#comment:5>
MacPorts <https://www.macports.org/>
Ports system for macOS