xbps-src by default uses xbps-uunshare(1) for chroot operations, that means that the linux kernel must support
user namespaces.

The beaglebone linux kernel in void is currently at 3.8.x, this branch does not support user namespaces.

As Christian Neukirchen said in this thread you'll have to switch to xbps-uchroot(1) instead in `void-packages/etc/conf`.

Cheers