Fix -Werror=implicit-function-declaration

unistd.h is needed for write, close and read

demo/searpc-demo-packet.h

@@ -4,6 +4,7 @@
 
 #include <stdint.h>
 #include <stdio.h>
+#include <unistd.h>
 #include <errno.h>
 
 #ifdef WIN32