os, shm: fcntl()'s third argument is integer, not pointer

All of these uses were attempting to set FD_CLOEXEC, which happens to be
(1<<0). Since flags is going to be aligned in memory, its address is
never going to have the low bit set, so we were never actually setting
what we meant to.

Fixes: xorg/xserver#1114
4 jobs for fcntl-flags in 4 minutes and 30 seconds (queued for 2 seconds)