[patch] Use std::__bool_constant instead of duplicating it

[Jonathan Wakely]

This is a tiny patch to use the new __bool_constant helper in
hashtable_policy.h instead of defining another identical alias.

Tested x86_64-linux, committed to trunk.


commit 3fa3e0af59fa4371f61e95eeaab240d3b974b62e
Author: Jonathan Wakely <jwak...@redhat.com>
Date:   Wed Apr 16 18:20:30 2014 +0100

    	* include/bits/hashtable_policy.h: Use __bool_constant.

diff --git a/libstdc++-v3/include/bits/hashtable_policy.h b/libstdc++-v3/include/bits/hashtable_policy.h
index 1251ef0..14bcca6 100644
--- a/libstdc++-v3/include/bits/hashtable_policy.h
+++ b/libstdc++-v3/include/bits/hashtable_policy.h
@@ -81,7 +81,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 
   // Helper type used to detect whether the hash functor is noexcept.
   template <typename _Key, typename _Hash>
-    struct __is_noexcept_hash : std::integral_constant<bool,
+    struct __is_noexcept_hash : std::__bool_constant<
 	noexcept(declval<const _Hash&>()(declval<const _Key&>()))>
     { };
 
@@ -211,9 +211,6 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
   template<bool _Cache_hash_code, bool _Constant_iterators, bool _Unique_keys>
     struct _Hashtable_traits
     {
-      template<bool _Cond>
-	using __bool_constant = integral_constant<bool, _Cond>;
-
       using __hash_cached = __bool_constant<_Cache_hash_code>;
       using __constant_iterators = __bool_constant<_Constant_iterators>;
       using __unique_keys = __bool_constant<_Unique_keys>;