"runqemu X" will use the system qemu if qemu-native hasn't been built which doesn't understand the -enable-gl option. We should always use the qemu-native binary and error if this was not built.
I pushed a patch earlier today which ensures that qemu (and the helper package) are built whenever the user builds an image for a qemu machine. 196f6f2d20a7926cadaec619f4422209e48a31bd qemu.inc: ensure helper programs are built when building for qemu machines QEMU machine images are useless without qemu-native and qemu-helper-native