exit_group.2: Use syscall(SYS_...); for system calls without a wrapper

<linux/unistd.h> is not needed.  We need <unistd.h> for syscall(),
and <sys/syscall.h> for SYS_exit_group.

Signed-off-by: Alejandro Colomar <alx.manpages@gmail.com>
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
1 file changed