Use __freadahead() instead of accessing inside FILE object.

Index: sys/sys.h
--- sys/sys.h.orig
+++ sys/sys.h
@@ -23,6 +23,11 @@
  *   terminal control: {USE_SGTTY,  USE_TERMIO, USE_TERMIOS}
  */
 
+#if defined(__OpenBSD__)
+#define USE_TERMIOS
+#define HAS_POLL
+#endif
+
 #if defined(sunos) \
  || defined(pureBSD43) \
  || defined(ultrix) \
@@ -69,7 +74,10 @@
 #define READYCC(fp)	(fp->_egptr - fp->_gptr)
 #endif
 #else
-#if defined(bsdi) || defined(__FreeBSD__)
+#ifdef __OpenBSD__
+#include <stdio_ext.h>
+#define READYCC(fp)	__freadahead(fp)
+#elif defined(bsdi) || defined(__FreeBSD__)
 #define READYCC(fp)	(fp->_r)
 #else
 #define READYCC(fp)	(fp->_cnt)
