Long-term we want to split system.h and include barriers part from
underlying target; for now copy that part to sysdep.
Signed-off-by: NAl Viro <viro@zeniv.linux.org.uk>
Signed-off-by: NH. Peter Anvin <hpa@zytor.com>

* turn asm/ldt.h into ldt.h; update the (very few) users
* take host_ldt.h into sysdep, kill symlink mess
* includes of asm/arch/ldt.h turn into asm/ldt.h now
Signed-off-by: NAl Viro <viro@zeniv.linux.org.uk>
Signed-off-by: NH. Peter Anvin <hpa@zytor.com>

We can't just plop asm/* into it - userland helpers are built with it
in search path and seeing asm/* show up there suddenly would be a bad
idea.
Signed-off-by: NAl Viro <viro@zeniv.linux.org.uk>
Signed-off-by: NH. Peter Anvin <hpa@zytor.com>