package/libcap-ng: add host variant

Qemu 5.0.0 recently switched to libcap-ng [1].
Add the host variant for host-qemu package.

[1] https://git.qemu.org/?p=qemu.git;a=commit;h=7e46261368d129c5ee8be927f5bcadc7ecd800d7



Signed-off-by: Romain Naour <romain.naour@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>