1. Download the appropriate release here:
https://github.com/protocolbuffers/protobuf/releases/tag/v3.5.1 <protobuf-all-3.5.1.tar.gz>
2. Unzip the folder
3. Enter the folder and run ./autogen.sh && ./configure && make
4. If you run into this error: autoreconf: failed to run aclocal: No such file or directory, run brew install autoconf && brew install automake. And run the command from step 3 again.
5. Then run these other commands. They should run without issues
$ make check
$ sudo make install
$ which protoc