Comment 0 for bug 1631597

Protobuf 3.1 contains the change:

* Moved default_instances to global variables. This allows default_instance addresses to be known at compile time.

This results if trying to compile against protobuf 3.1 that there will be errors like:
undefined reference to `mir::protobuf::SurfaceId_default_instance_'

and similar missing references to default_instance

I was able to workaround this problem by dropping all references to default_instance entries in src/protobuf/symbols.map
but probably this needs a better solution in upstream Mir development