From https://gcc.gnu.org/bugzilla/show_bug.cgi?id=87822
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Wed Oct 31 13:03:25 2018 +0000

    PR libstdc++/87822 fix layout change for nested std::pair
    
    The introduction of the empty __pair_base base class for PR 86751
    changed the layout of std::pair<std::pair<...>, ...>. The outer pair and
    its first member both have a base class of the same type, which cannot
    exist at the same address. This causes the first member to be at a
    non-zero offset.
    
    The solution is to make the base class depend on the template
    parameters, so that each pair type has a different base class type,
    which allows the base classes of the outer pair and its first member to
    have the same address.
    
            PR libstdc++/87822
            * include/bits/stl_pair.h (__pair_base): Change to class template.
            (pair): Make base class type depend on template parameters.

diff --git a/libstdc++-v3/include/bits/stl_pair.h b/libstdc++-v3/include/bits/stl_pair.h
index a30b630b4fd..5a4823ab018 100644
--- a/libstdc++-v3/include/bits/stl_pair.h
+++ b/libstdc++-v3/include/bits/stl_pair.h
@@ -183,7 +183,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
   };
 #endif // C++11
 
-  class __pair_base
+  template<typename _U1, typename _U2> class __pair_base
   {
 #if __cplusplus >= 201103L
     template<typename _T1, typename _T2> friend struct pair;
@@ -202,7 +202,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
    */
   template<typename _T1, typename _T2>
     struct pair
-    : private __pair_base
+    : private __pair_base<_T1, _T2>
     {
       typedef _T1 first_type;    /// @c first_type is the first bound type
       typedef _T2 second_type;   /// @c second_type is the second bound type