Add more to util.h to help with amalg build.
#ifndef JANET_UTIL_H_defined
#define JANET_UTIL_H_defined
+#include <stdio.h>
+#include <errno.h>
+#ifndef JANET_WINDOWS
+#include <sys/wait.h>
+#endif
+
#ifndef JANET_AMALG
#include <janet.h>
#endif
