Proposed resolution:

This wording is relative to N4830.

1. Modify [iterator.requirements.general] as indicated:

   -16- Iterators are called constexpr iterators if all operations provided to meet iterator category requirements are constexpr functions., except for

   1. (16.1) — a pseudo-destructor call ([expr.prim.id.dtor]), and

   2. (16.2) — the construction of an iterator with a singular value.