/// isSizedDerivedType - Derived types like structures and arrays are sized
/// iff all of the members of the type are sized as well. Since asking for
/// their size is relatively uncommon, move this operation out of line.
/// isSizedDerivedType - Derived types like structures and arrays are sized
/// iff all of the members of the type are sized as well. Since asking for
/// their size is relatively uncommon, move this operation out of line.