reverse-ramdisk.c: include unistd.h

c-programming/reverse-ramdisk.c

@@ -18,6 +18,7 @@ To-Do: error handling on line 184, function fread()
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
+#include <unistd.h>
 
 #ifdef DEBUG
 # define line_fail(x) do { \