Proposed resolution:

This wording is relative to N4830.

1. Modify [memory.syn], header <memory> synopsis, as indicated:

   namespace std {
     […]
     
     // [specialized.destroy], destroy
     template<class T>
       constexpr void destroy_at(T* location);
     template<class ForwardIterator>
       constexpr void destroy(ForwardIterator first, ForwardIterator last);
     template<class ExecutionPolicy, class ForwardIterator>
       constexpr void destroy(ExecutionPolicy&& exec, // see [algorithms.parallel.overloads]
                              ForwardIterator first, ForwardIterator last);
     template<class ForwardIterator, class Size>
       constexpr ForwardIterator destroy_n(ForwardIterator first, Size n);
     template<class ExecutionPolicy, class ForwardIterator, class Size>
       constexpr ForwardIterator destroy_n(ExecutionPolicy&& exec, // see [algorithms.parallel.overloads]
                                           ForwardIterator first, Size n);  
     […]
   }
   

[ 2019-11 Marked as 'Ready' during Monday issue prioritization in Belfast ]

This issue was submitted as editorial issue cplusplus/draft#3181 but is considered non-editorial.

P0784R7, approved in Cologne, added "constexpr" markers to the overloads of destroy and destroy_n taking an ExecutionPolicy parameter. This seems to be in error; parallel algorithms should not be marked "constexpr". (None of the parallel algorithms in <algorithm> is marked "constexpr".)