segfault when devtools::load_all("flowWorkspace") multiple times

[mikejiang]

It is triggered by dynamic linked libprotobuf(ad22c36) and won't necessarily affect end users since multiple library(flowWorkspace) calls won't cause the lib to be reloaded.

Loading flowWorkspace
[libprotobuf ERROR google/protobuf/descriptor_database.cc:57] File already exists in database: GatingSet.proto
[libprotobuf FATAL google/protobuf/descriptor.cc:1018] CHECK failed: generated_database_->Add(encoded_file_descriptor, size): 
terminate called after throwing an instance of 'google::protobuf::FatalException'
  what():  CHECK failed: generated_database_->Add(encoded_file_descriptor, size): 
Aborted (core dumped)

It's been discussed here protocolbuffers/protobuf/issues/4126 and I will try to build GatingSet.pb.cc as shared lib as well to see if it will address the issue.