Due to a little boondoggle, some users may have trouble upgrading
mesa because pacman can't figure out the dependency tree. If this is the case, and pacman tells you that it can't satisfy dependencies on
mesa-libgl, then you should be able to resolve this by manually telling pacman that the resolution is
# pacman -Su libglvnd
Additionally, multilib users may need to manually downgrade from the no-longer-existing
libre-multilib/lib32-mesa and friends to
multilib/lib32-mesa and friends.