add support for privilege separation

Privileged helper that will perform adjtime(), settimeofday(), bind() on
behalf of chronyd when running as non-root user.

sysincl.h

@@ -53,6 +53,7 @@
 #include <sys/types.h>
 #include <sys/un.h>
 #include <sys/shm.h>
+#include <sys/wait.h>
 #include <syslog.h>
 #include <time.h>
 #include <unistd.h>