I’ve been with ATI/AMD since 2001, i don’t think they are going to pay for a such a license.
Things have improved apparently:
https://mesa-freeworld.github.io/mesa-nonfree/
Packages are now pre compiled and you can even add it as an unofficial repository.
sudo pacman-key --recv-keys B728DB23B92CB01B && sudo pacman-key --lsign-key B728DB23B92CB01B
sudo sh -c "curl -s https://mesa-freeworld.github.io/mesa-nonfree/$(pacman-mirrors -G)/ > /etc/pacman.d/mesa-nonfree.pre.repo.conf"
sudo sed -i '/^\[core\]/i \Include = /etc/pacman.d/mesa-nonfree.pre.repo.conf\n' /etc/pacman.conf