gui/Flirc.1.0.2-alpha/linux/Flirc: error while loading shared libraries: libXt.so.6: cannot open shared object file: No such file or directory
This is because the GUI is built with 32bit libraries. A 32 bit application can generally run on a 64 operating system assuming the operating system has the 32 bit libraries.
Just install the 32b compatibility libraries. As an example, on Ubuntu, this can be done by:
sudo apt-get install ia32-libs