Added stdbool.h for c99 compilers in drake.c

rigs/drake/drake.c

@@ -23,6 +23,7 @@
 #include <stdlib.h>
 #include <string.h>  /* String function definitions */
 #include <unistd.h>  /* UNIX standard function definitions */
+#include <stdbool.h>
 
 #include "hamlib/rig.h"
 #include "serial.h"