it may be a structure, not an integer
Pointed out on the list by Scott Ratliff <scottr@carsinfo.com>,
while doing HPUX builds
#if HAVE_PTHREAD_H
#include <pthread.h>
-typedef pthread_t child_pid_t ;
+typedef pthread_t child_pid_t;
#define child_kill pthread_kill
#else
typedef pid_t child_pid_t;
#define child_kill kill
#endif
-#define NO_SUCH_CHILD_PID (0)
+#define NO_SUCH_CHILD_PID (child_pid_t) (0)
#ifndef NDEBUG
#define REQUEST_MAGIC (0xdeadbeef)