ARMLFS has a build of the FPGA toolchain needed for using the glasgow, plus other core dependencies.

Do this first:

pacman -S python-libusb1 yosys nextpnr-ice40

Then follow the instructions for Arch at glasgow-embedded.org, though you can skip install of the builtin toolchain, like so:

pipx install -e 'glasgow/software'

Happy Hacking :)