Re: MAX31855 Library on Arduino Due
In general terms, that's a hardware compatibility issue.
The file "avr/pgmspace.h" contains information about the ATmega series of microcontrollers, which are used in the Uno and other main-line Arduinos. The Due uses an ARM chip, so information about the AVR memory space isn't relevant there.
I'm not sure exactly what job that header has in the MAX31855 library, so I'll pass this to our Due expert to see if he has any suggestions.