Add symbols from sys/mount.h for older glibc.

MNT_DETACH and MNT_EXPIRE are not available with glibc before 2.10.

UMOUNT_NOFOLLOW is not available with glibc before 2.12.

This patches fixes these build errors with older glibc.

syscalls/umount.c:16: error: ‘MNT_DETACH’ undeclared here (not in a function)
syscalls/umount.c:16: error: ‘MNT_EXPIRE’ undeclared here (not in a function)
syscalls/umount.c:16: error: ‘UMOUNT_NOFOLLOW’ undeclared here (not in a function)

Signed-off-by: Vinson Lee <vlee@twitter.com>
can.c: Include compat.h.

This patch fixes these build errors with glibc before 2.10.

net/can.c: In function ‘can_gen_sockaddr’:
net/can.c:17: error: ‘AF_CAN’ undeclared (first use in this function)
net/can.c:17: error: (Each undeclared identifier is reported only once
net/can.c:17: error: for each function it appears in.)

Signed-off-by: Vinson Lee <vlee@twitter.com>