Hi thomasricci,
I'm afraid the SoftwareSerial library isn't supported by the Galileo (Gen 1 and Gen 2). You can check the release notes in order to know which libraries are currently supported: Intel® Galileo Gen 2 Release Notes. I'll recommend you also a couple of posts where the users have discussed about the SoftwareSerial library topic:
SoftwareSerial library doesn't work
Is there a software serial library for Galileo?
Check the post, they might be helpful for you. Have a nice day!
Regards,
Diego.