AR refers to "armar" which is the ARM utility for creating libraries. FR refers to "fromelf" which is a tool for inspecting ELF objects and images, for converting them to other formats. I haven't got a copy of the example to hand, but I doubt it actually needs either.
Switch to GCC/GNU tools I foresee two problems. GAS (GNU assembler tool) and armasm (ARM's assembler tool) use different syntax. Which makes the .s files for one incompatible with the other. Meaning you'll have to port it. It's not too difficult (from limited past experience) but can be fiddly. Helps if you know one of the syntaxes well to start with.
THe other potential problem is libraries. The calls you make to set up and initialise the C library are different.
Many thanks for your helpful reply.
Great, I believe I can port the ARM .as files into the GNU .as files and I am aware of their major syntax differences.
Could you please provide more information about the issue of Libraries or route me to a helpful related document.
Thank you very much.