LWG3454 pointer_traits::pointer_to should be constexpr

[pointer.traits] pointer_to already declared constexpr in synopsis.

Author: burblebee

source/memory.tex

@@ -850,7 +850,7 @@
 
 \indexlibrarymember{pointer_to}{pointer_traits}%
 \begin{itemdecl}
-static pointer pointer_traits::pointer_to(@\seebelow@ r);
+static constexpr pointer pointer_traits::pointer_to(@\seebelow@ r);
 static constexpr pointer pointer_traits<T*>::pointer_to(@\seebelow@ r) noexcept;
 \end{itemdecl}