[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 ryandesign):

 So I guess what wasn't said in the ticket, but which I recall from
 previous discussion, is that protobuf3-cpp requires C++11 now, so
 everything that uses it does too, and needs the cxx11 1.1 portgroup at
 least.

 Replying to [comment:5 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...

 As always, don't force specific compilers (e.g. by setting
 `compiler.whitelist` or `configure.compiler`). Instead, use
 `compiler.blacklist` to list the compilers that don't work, and if
 necessary, add a working compiler to `compiler.fallback`.

 The problem you pointed out with caffe was that we needed to add
 `-std=c++11` to the compile flags somewhere. Since protobuf3-cpp
 apparently requires C++11 now, shouldn't it be arranging for `-std=c++11`
 to appear in the compile flags?

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Ticket URL: <https://trac.macports.org/ticket/57117#comment:6>
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