init.h started breaking now for some reason.  It turns out that there wasn't a
definition of __used.  Fixed this by copying the relevant stuff from
compiler.h in the userspace case, and including compiler.h in the kernel case.

[xiyou.wangcong@gmail.com: added definition of __section]
Signed-off-by: NJeff Dike <jdike@linux.intel.com>
Cc: WANG Cong <xiyou.wangcong@gmail.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>