Hmm,

avr/io.h should not be needed, so you should be able to remove that without issues. It’s probably a relic from an old version.

Why it won’t work on a Galileo I don’t know. The ET library uses the Stream class and should be portable with the Arduino IDE. Actually, maybe not. The Galileo may not be able to handle the malloc memory initialization. I’d have to get my hands on one or someone else try modding the library to not dynamically alloicate memory for the receive buffer.