A la rev. 1.36, define CONS_CLRHIST here if it isn't already since

this is a build tool, so it has to build on 4.x with the old headers.

usr.sbin/kbdcontrol/kbdcontrol.c

@@ -44,12 +44,16 @@ static const char rcsid[] =
 #include "lex.h"
 
 /*
- * PASTE isn't defined in 4.x, but we need it to bridge to 5.0-current
- * so define it here as a stop gap transition measure.
+ * PASTE and CONS_CLRHIST are't defined in 4.x, but we need them to
+ * bridge to 5.0-current so define them here as a stop gap transition
+ * measure.
  */
 #ifndef PASTE
 #define PASTE		0xa3		/* paste from cut-paste buffer */
 #endif
+#ifndef	CONS_CLRHIST
+#define CONS_CLRHIST	_IO('c', 10)
+#endif
 
 char ctrl_names[32][4] = {
 	"nul", "soh", "stx", "etx", "eot", "enq", "ack", "bel",