Description: kernel/exit.c: avoid undefined behaviour when calling wait4()
References:
 https://news.ycombinator.com/item?id=2972021
 http://lkml.kernel.org/r/1497264618-20212-1-git-send-email-zhongjiang@huawei.com
Notes:
 bwh> This looks very unlikely to have any security impact in reality.
Bugs:
upstream: released (4.13-rc1) [dd83c161fbcc5d8be637ab159c0de015cbff5ba4]
4.9-upstream-stable: released (4.9.101) [04103c29b6cc1ffcf9efe167a07e882be68f8367]
3.16-upstream-stable: ignored "Minor issue"
3.2-upstream-stable: ignored "Minor issue"
sid: released (4.13.4-1)
4.9-stretch-security: released (4.9.107-1)
3.16-jessie-security: ignored "Minor issue"
3.2-wheezy-security: ignored "Minor issue"