For Android build you need to set up your local work environment according Google's recommendations. Probably You need to install additional packets. Please use ...

repo init -u git://github.com/minimal-manifest-twrp/platform_manifest_twrp_omni.git -b twrp-8.1 repo sync . build/envsetup.sh lunch omni_T8116-eng mka recoveryimage ...

Even if it’s early days, since most documentation and source code is already available for AllWinner A20, we should see Linux run on such device very soon, probably with proper GPU support, but no VPU ...