I'm also using arch and got it working without major issues. If I recall correctly, you'll just have to:
If you get an error on
make: arm-none-eabi-gcc: Command not found
make: *** [../chibios/os/ports/GCC/ARMCMx/rules.mk:190: build/obj/arm_bitreversal2.o] Error 127
It probably means that both
lib32-bzip2 were not installed. For getting them in arch (64), you'll have to enable the multilib repository. See https://wiki.archlinux.org/index.php/multilib
Hope it helps!