Revert "Update aosp/master libcxx rebase to r263688"

The world is burning.

This reverts commit c004fd909c006eec55077c52ee119e1fa338c9e9, reversing
changes made to 1418e4163da4bb0b9e3fe496e51c23a0dce399d9.
diff --git a/include/shared_mutex b/include/shared_mutex
index 923fe07..dcb9394 100644
--- a/include/shared_mutex
+++ b/include/shared_mutex
@@ -319,25 +319,25 @@
 
     _LIBCPP_INLINE_VISIBILITY
     explicit shared_lock(mutex_type& __m)
-        : __m_(_VSTD::addressof(__m)),
+        : __m_(&__m),
           __owns_(true)
         {__m_->lock_shared();}
 
     _LIBCPP_INLINE_VISIBILITY
     shared_lock(mutex_type& __m, defer_lock_t) _NOEXCEPT
-        : __m_(_VSTD::addressof(__m)),
+        : __m_(&__m),
           __owns_(false)
         {}
 
     _LIBCPP_INLINE_VISIBILITY
     shared_lock(mutex_type& __m, try_to_lock_t)
-        : __m_(_VSTD::addressof(__m)),
+        : __m_(&__m),
           __owns_(__m.try_lock_shared())
         {}
 
     _LIBCPP_INLINE_VISIBILITY
     shared_lock(mutex_type& __m, adopt_lock_t)
-        : __m_(_VSTD::addressof(__m)),
+        : __m_(&__m),
           __owns_(true)
         {}
 
@@ -345,7 +345,7 @@
         _LIBCPP_INLINE_VISIBILITY
         shared_lock(mutex_type& __m,
                     const chrono::time_point<_Clock, _Duration>& __abs_time)
-            : __m_(_VSTD::addressof(__m)),
+            : __m_(&__m),
               __owns_(__m.try_lock_shared_until(__abs_time))
             {}
 
@@ -353,7 +353,7 @@
         _LIBCPP_INLINE_VISIBILITY
         shared_lock(mutex_type& __m,
                     const chrono::duration<_Rep, _Period>& __rel_time)
-            : __m_(_VSTD::addressof(__m)),
+            : __m_(&__m),
               __owns_(__m.try_lock_shared_for(__rel_time))
             {}