Separate VM instruction for variable declaration (OP_DECLARE).

include/ph7int.h

@@ -1389,6 +1389,7 @@ enum iErrCode {
 enum ph7_vm_op {
 	PH7_OP_DONE =   1,   /* Done */
 	PH7_OP_HALT,         /* Halt */
+	PH7_OP_DECLARE,      /* Declare a variable */
 	PH7_OP_LOAD,         /* Load memory object */
 	PH7_OP_LOADC,        /* Load constant */
 	PH7_OP_LOAD_IDX,     /* Load array entry */