Optimized debugging API to reduce code size.

diff --git a/msdos/ioports.c b/msdos/ioports.c
index 29e2329..3862af9 100644
--- a/msdos/ioports.c
+++ b/msdos/ioports.c
@@ -13,6 +13,7 @@
 
 #include <ctype.h>
 #include <stdlib.h>
+#include <stdio.h>
 #include <string.h>
 #include <time.h>
 #include <unistd.h>