Description: fix infoleak in waitid(2)
References:
 https://grsecurity.net/~spender/exploits/wait_for_kaslr_to_be_effective.c
 https://twitter.com/_argp/status/914021130712870912
 https://twitter.com/grsecurity/status/914079864478666753
Notes:
 carnil> Fixes ce72a16fa705f960ca2352e95a7c5f4801475e75 (4.13-rc1)
Bugs:
upstream: released (4.14-rc3) [6c85501f2fabcfc4fc6ed976543d252c4eaf4be9]
4.9-upstream-stable: N/A "Vulnerable code introduced in 4.13-rc1"
3.16-upstream-stable: N/A "Vulnerable code introduced in 4.13-rc1"
3.2-upstream-stable: N/A "Vulnerable code introduced in 4.13-rc1"
sid: N/A "Vulnerable code not present"
4.9-stretch-security: N/A "Vulnerable code not present"
3.16-jessie-security: N/A "Vulnerable code not present"
3.2-wheezy-security: N/A "Vulnerable code not present"