package/qemu: add optional dependency on nettle

Qemu can optionally depend on nettle if available, so we should take
into account this optional dependency.

Cc: Florian Wolters <florian@florian-wolters.de>
Signed-off-by: Alexander Dahl <post@lespocky.de>
[Thomas: reword commit log, so that it makes sense in the context of
upstream Buildroot]
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
1 file changed