[memory.syn] Add reinterpret_pointer_cast to synopsis

Author: jwakely

source/utilities.tex

@@ -7172,6 +7172,8 @@
     shared_ptr<T> dynamic_pointer_cast(const shared_ptr<U>& r) noexcept;
   template<class T, class U>
     shared_ptr<T> const_pointer_cast(const shared_ptr<U>& r) noexcept;
+  template<class T, class U>
+    shared_ptr<T> reinterpret_pointer_cast(const shared_ptr<U>& r) noexcept;
 
   // \ref{util.smartptr.getdeleter}, \tcode{shared_ptr} \tcode{get_deleter}
   template<class D, class T>