Include <stddef.h> everywhere ptrdiff_t is used

ptrdiff_t is defined in <stddef.h>

src/aclients.c

@@ -76,6 +76,7 @@
 #include <stdio.h>
 #include <assert.h>
 #include <ctype.h>
+#include <stddef.h>
 #include <string.h>
 #include <time.h>
 

src/dwgpsd.c

@@ -45,6 +45,7 @@
 #include <errno.h>
 #include <time.h>
 #include <math.h>
+#include <stddef.h>
 
 #if __WIN32__
 #error Not for Windows

src/dwgpsnmea.c

@@ -54,6 +54,7 @@
 #include <string.h>
 #include <errno.h>
 #include <time.h>
+#include <stddef.h>
 
 
 #include "textcolor.h"

src/kissnet.c

@@ -113,6 +113,7 @@
 #include <stdio.h>
 #include <assert.h>
 #include <string.h>
+#include <stddef.h>
 
 
 #include "tq.h"

src/kissutil.c

@@ -56,6 +56,7 @@
 #include <stdio.h>
 #include <assert.h>
 #include <ctype.h>
+#include <stddef.h>
 #include <string.h>
 #include <getopt.h>
 #include <dirent.h>

src/recv.c

@@ -88,6 +88,7 @@
 #include <unistd.h>
 #include <stdlib.h>
 #include <string.h>
+#include <stddef.h>
 #include <sys/types.h>
 //#include <sys/stat.h>
 //#include <sys/ioctl.h>

src/server.c

@@ -145,6 +145,7 @@
 #include <string.h>
 #include <time.h>
 #include <ctype.h>
+#include <stddef.h>
 
 #include "tq.h"
 #include "ax25_pad.h"

src/xmit.c

@@ -60,6 +60,7 @@
 #include <string.h>
 #include <math.h>
 #include <errno.h>
+#include <stddef.h>
 
 #include "direwolf.h"
 #include "ax25_pad.h"