kvm tools: mark usages functions as NORETURN

kvm tools: mark usages functions as NORETURN

It will help for simplifying codes like this:

{
	if (cond == NULL)
		NORETURN_func();

	/* use cond safely, it is not NULL and don't need to check it again */
}

It also helps for readability.

Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
Signed-off-by: Pekka Enberg <penberg@kernel.org>