Hi Alberto, thank you for testing ns8 on the ARM architecture. We must confess we didn’t it yet!
The pip command didn’t find a package already compiled for ARM and is attempting to compile it with GCC.
After solving this issue, probably you’re finding more!
I can’t help you now to sort it out. Hopefully someone interested in the ARM support will step in 
I’d like multi-arch support for ns8 but it’s not my priority. It’s maybe better to state it somewhere…