Wayland and Weston are now provided by ArchLinux, this means the
hawaii repository is not going to provide them anymore.
ArchLinux wiki has more information about it.
pacman -R weston-git
pacman -Syu cairo
If you previously installed
mesa-full-wayland you have to install
sudo pacman --needed -Syu mesa libdrm libgl libglapi libegl libgles intel-dri nouveau-dri libgbm khrplatform-devel
pacman -Syu wayland weston