Tael-arc is the armv8 overlay for ARCVM; see the tael and project-termina overlays for details. This board is almost identical to tael with the one difference that the guest kernel config points to arm64_arcvm_defconfig rather than chromiumos-container-vm-arm64_defconfig.
This board is only used to generate the guest kernel prebuilts, which are then manually checked in to the Android tree.