[Bug libstdc++/61390] New: error in nested template parameter in ext/pb_ds header file

["john.tromp at gmail dot com" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61390

            Bug ID: 61390
           Summary: error in nested template parameter in ext/pb_ds header
                    file
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: minor
          Priority: P3
         Component: libstdc++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: john.tromp at gmail dot com

Include file ext/pb_ds/detail/bin_search_tree_/traits.hpp has two occurances
(lines 53 and 160 in 4.8.1) of
template<typename Key,
         ...
         class Cmp_Fn,
         template<typename Node_CItr,
                  class Node_Itr,
                  class Cmp_Fn,
                  typename _Alloc>
         class Node_Update,
         class Node,
         typename _Alloc>
...

on which some compilers in c++11 mode (e.g. clang++ -std=c++11) rightfully
raise an error since the second declaration of 'Cmp_Fn' shadows the first.

This is trivially avoided by renaming the second as _Cmp_Fn