helpers/envkernel.sh: Fix "Unable to deduce build architecture"
After an abuild update in Alpine envkernel.sh now throws an error when activating envkernel:
ash: to: not found
Run 'pmbootstrap log' for details.
This happens because functions.sh fails with:
Unable to deduce build architecture. Install apk-tools, or set CBUILD.
For now it seems to be enough to set CBUILD appropriately to make it work again.
This is based on a suggestion from @lorendb.