Fix cppcheck warning

code/tools/lcc/lburg/gram.y

@@ -199,4 +199,5 @@ void yywarn(char *fmt, ...) {
 		fprintf(stderr, "line %d: ", yylineno);
 	fprintf(stderr, "warning: ");
 	vfprintf(stderr, fmt, ap);
+	va_end(ap);
 }