Fix constexpr annotations.

Author: ichaer

libcxx/include/__algorithm/iterator_operations.h

@@ -91,13 +91,13 @@ struct _IterOps<_ClassicAlgPolicy> {
   // it's unclear whether _Iter has a difference_type and whether that's signed, so we play it safe:
   // use the incoming type for returning and steer clear of negative overflows
   template <class _Iter, class _Distance>
-  _LIBCPP_HIDE_FROM_ABI constexpr static _Distance advance(_Iter& __iter, _Distance __count, const _Iter& __sentinel) {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 static _Distance advance(_Iter& __iter, _Distance __count, const _Iter& __sentinel) {
     return _IterOps::__advance(__iter, __count, __sentinel, typename iterator_traits<_Iter>::iterator_category());
   }
 
   // advance with sentinel, a la std::ranges::advance -- InputIterator specialization
   template <class _InputIter, class _Distance>
-  _LIBCPP_HIDE_FROM_ABI constexpr static _Distance
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 static _Distance
   __advance(_InputIter& __iter, _Distance __count, const _InputIter& __sentinel, input_iterator_tag) {
     _Distance __dist{};
     for (; __dist < __count && __iter != __sentinel; ++__dist)
@@ -107,7 +107,7 @@ struct _IterOps<_ClassicAlgPolicy> {
 
   // advance with sentinel, a la std::ranges::advance -- BidirectionalIterator specialization
   template <class _BiDirIter, class _Distance>
-  _LIBCPP_HIDE_FROM_ABI constexpr static _Distance
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 static _Distance
   __advance(_BiDirIter& __iter, _Distance __count, const _BiDirIter& __sentinel, bidirectional_iterator_tag) {
     _Distance __dist{};
     if (__count >= 0)