Marshall Clow's fix for Bug 8421.

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@122825 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/include/map b/include/map
index 64c2808..387c6b5 100644
--- a/include/map
+++ b/include/map
@@ -350,7 +350,7 @@
 class __map_value_compare
     : private _Compare
 {
-    typedef pair<_Key, _Tp> _P;
+    typedef pair<typename std::remove_const<_Key>::type, _Tp> _P;
     typedef pair<const _Key, _Tp> _CP;
 public:
     _LIBCPP_INLINE_VISIBILITY
@@ -393,7 +393,7 @@
 {
     _Compare comp;
 
-    typedef pair<_Key, _Tp> _P;
+    typedef pair<typename std::remove_const<_Key>::type, _Tp> _P;
     typedef pair<const _Key, _Tp> _CP;
 
 public: