HomeBrew versions has been removed and formulaes have been emptied. Therefore, my advice is to install it manually following the following steps.
For the time being you will need to build and install the Protocol Buffers toolset manually.
Download source code: https://github.com/google/protobuf/releases/download/v2.4.1/protobuf-2.4.1.tar.gz
tar xvfz protobuf-2.4.1.tar.gz
cd protobuf-2.4.1
Run ./configure
Edit src/google/protobuf/message.cc, add #include at the top of the file
Run make
command from root of the folder, i.e. protobuf-2.4.1/
Run sudo make install
Run /usr/local/bin/protoc --version
to check the version of protobuf compiler version
The terminal output should be:
Version: libprotoc 2.4.1