mini-os: use BSD sys/queue.h instead of Linux list.h

mini-os: use BSD sys/queue.h instead of Linux list.h

The latter is GPL which makes the whole of mini-os GPL rather than BSD
as intended. In tree users are all GPL or GPL-compatible but we should
fix this so that mini-os is BSD. Do so by using the same BSD
sys/queue.h as we use in libxl.

Tested with the builtin mini-os test app and qemu stubdomain, both of which
appear to still function as expected.

Move tools/libxl/external and the associated sed script to
tools/include/xen-external to allow more sensible access from mini-os.

Also add s/NULL/0/ in the sed script due to NULL not always being
defined in stubdom code when mini-os/wait.h is included.

As well as the obvious ABI changes there are a few API updates
associated with the change:

  - struct rw_semaphore.wait_list is unused
  - remove_waiter needs to take the wait_queue_head

The latter requires a qemu update, so there is also a QEMU_TAG
update in this changeset.

I sprinkled some extra-emacs local variables around the files I edited
which didn't have them.

I think this should be backported to the stable branches since
external users of mini-os may have been mislead into thinking they
could safely link mini-os against GPL-incompatible code.

Signed-off-by: Ian Campbell <ian.campbell@citrix.com>
Committed-by: Ian Jackson <Ian.Jackson@eu.citrix.com>