I see, that you already managed to go through the Qt deployment and RespeQt compilation process. Great
In the mean time I prepared a complete RespeQt package (containing all required libraries) for Raspberry Pi.
You just prepare the SD card with the Raspbian Jessie Image, start the Raspberry Pi and unpack the following file into the home directory (home/pi):
Then you open the terminal and type in:
In the RespeQt settings, you have to provide the device name, for a SIO2PC/USB cable, it is usually /dev/ttyUSB0
By the way, 3 years ago I worked on a small SIO2PI project for the RaspberryPi (http://atariage.com/...y/#entry2698490).
The goal was to use the existing serial port on the RPI (/dev/ttyAMA0).
The cable requires a simple level shifter (3.3V <-> 5V).
I used a GPIO port for hardware handshaking (so I modified AspeQt at that time), but today with "NONE" and "SOFTWARE" handshake it is not necessary any more.
Per default Raspberry Pi uses the serial port for tracing and for a serial console. Both functions have to be disabled in order to use /dev/ttyAMA0 with RespeQt.
This opens a new possibility (not related to the RespeQt) to use the ATARI as a terminal for Raspberry PI. I will desribe my experience in a new thread.