xen: arm: include public/xen.h in foreign interface checking

xen: arm: include public/xen.h in foreign interface checking

mkheader.py doesn't cope with
	struct foo { };
so add a newline.

Define unsigned long and long to a non-existent type on ARM so as to catch
their use.

Teach mkheader.py to cope with structs which are ifdef'd. This cannot cope
with #defines between the #ifdef and the struct definitions, so move
MAX_GUEST_CMDLINE to be next to its only usage.

Signed-off-by: Ian Campbell <ian.campbell@citrix.com>
Acked-by: Keir Fraser <keir@xen.org>
Acked-by: Ian Jackson <ian.jackson@eu.citrix.com>