Mojave (10.14) setting environment variables
The answer to this one in Mojave is to create a named file in /etc/paths.d, for instance

vi /etc/paths.d/local_bin


Put

/usr/local/bin


in the file, save and quit. Start another terminal window and it will be on your path.

I have one for MacPorts

$ cat MacPorts 
/opt/local/bin