To fix older compilers again (this was the case in hb_array_t).

hb-ot-layout-common.hh:1353: note: candidate 2: operator[](T*, int) <built-in>
hb-ot-layout-common.hh:1354: error: ISO C++ says that these are ambiguous, even though the worst conversion for the first is better than the worst conversion for the second:
hb-iter.hh:63: note: candidate 1: Item& hb_iter_t<Iter, Item>::operator[](unsigned int) const [with Iter = hb_array_t<const OT::IntType<short unsigned int, 2u> >, Item = const OT::IntType<short unsigned int, 2u>]
hb-ot-layout-common.hh:1354: note: candidate 2: operator[](T*, int) <built-in>
hb-ot-layout-common.hh: In member function 'bool OT::ClassDef::serialize(hb_serialize_context_t*, hb_array_t<const OT::IntType<short unsigned int, 2u> >, hb_array_t<const OT::IntType<short unsigned int, 2u> >)':
hb-ot-layout-common.hh:1490: error: ISO C++ says that these are ambiguous, even though the worst conversion for the first is better than the worst conversion for the second:
hb-iter.hh:63: note: candidate 1: Item& hb_iter_t<Iter, Item>::operator[](unsigned int) const [with Iter = hb_array_t<const OT::IntType<short unsigned int, 2u> >, Item = const OT::IntType<short unsigned int, 2u>]
hb-ot-layout-common.hh:1490: note: candidate 2: operator[](T*, int) <built-in>