Fix implicit declaration of functions.
--- ttcp.c.orig	2021-05-11 19:48:58.000000000 -0500
+++ ttcp.c	2021-05-11 20:17:33.000000000 -0500
@@ -45,6 +45,8 @@
 /* #define SYSV */	/* required on SGI IRIX releases before 3.3 */
 
 #include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
 #include <signal.h>
 #include <ctype.h>
 #include <errno.h>
@@ -55,6 +57,7 @@
 #include <arpa/inet.h>
 #include <netdb.h>
 #include <sys/time.h>		/* struct timeval */
+#include <unistd.h>
 
 #if defined(SYSV)
 #include <sys/times.h>