sys/cddl/Makefile: Workaround complaints of userland inclusion

Workaround the following error message:

 error 'This file should not be included by userland programs'

Signed-off-by: Edward O'Callaghan <eocallaghan@alterapraxis.com>
cmd/zfs/zfs_main.c: fix jail.h include

Signed-off-by: Edward O'Callaghan <eocallaghan@alterapraxis.com>
sys/cpu/x86_64: Missing atomic_{add,subtract}_64 in atomic.h

Signed-off-by: Edward O'Callaghan <eocallaghan@alterapraxis.com>
sysmacros.h redefines howmany() that is already in param.h

This could be done better..

Signed-off-by: Edward O'Callaghan <eocallaghan@alterapraxis.com>
include/rpc/xdr.h: Partial sync with FreeBSD

Signed-off-by: Edward O'Callaghan <eocallaghan@alterapraxis.com>
cddl/contrib/*/thread.h: Internalise thread_t as it conflicts

Signed-off-by: Edward O'Callaghan <eocallaghan@alterapraxis.com>
sys/cddl/compat/opensolaris: Stub out (WIP)

Stub out function so we can continue to build..

Signed-off-by: Edward O'Callaghan <eocallaghan@alterapraxis.com>