chore: import upstream snapshot with attribution

examples/c/waitpid.c

@@ -0,0 +1,17 @@
+#include <sys/wait.h>
+#include <unistd.h>
+#include <errno.h>
+#include <stdio.h>
+
+int main()
+{
+	int status;
+
+	pid_t p = getpid();
+	// waitpid takes a children's pid, not the current process one
+	// if the pid is not a children of the current process, it returns -ECHILD
+	pid_t res = waitpid(1001, &status, WNOHANG);
+
+	printf("res is %d, p is %d and errno is %d\n", res, p, errno);
+
+}