define a new structure type index - index of new structure type If another structure has the specified index, then index of that structure and all other structures will be increentedfreeing the specifed index. If index is == -1, then the biggest index number will be used. See get_first_struc_idx() for the explanation of structure indices and IDs.name - name of the new structure type.is_union - 0: structure 1: unionreturns: -1 if can't define structure type because of bad structure name: the name is ill-formed or is already used in the program. otherwise returns ID of the new structure typelong add_struc(long index, string name, long is_union);