qemu-xen-trad: fix sys-queue.h usage on BSD systems

qemu-xen-trad: fix sys-queue.h usage on BSD systems

BSD systems already have a sys/queue.h file, which has more macros
than the one Qemu uses, and some header files depend on having that
macros defined (sys/disk.h for example). Disable sys-queue.h on BSD
systems and include the native one.

This is not a backport because the original patch is too dificult to
backport, it's commit 72cf2d4f0e181d0d3a3122e04129c58a95da713e.

Doing a diff -bB shows that the Qemu version is just a stripped
version of the original NetBSD header, with many macros removed, but
no new ones added.

Signed-off-by: Roger Pau Monne <roger.pau@citrix.com>
Acked-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
Acked-by: Ian Jackson <ian.jackson@eu.citrix.com>