Consistently label __bit_array as a struct, not a class.

llvm-svn: 162108
diff --git a/libcxx/include/bitset b/libcxx/include/bitset
index 55b5575..0c40b9b 100644
--- a/libcxx/include/bitset
+++ b/libcxx/include/bitset
@@ -159,7 +159,7 @@
     friend class __bit_const_reference<__bitset>;
     friend class __bit_iterator<__bitset, false>;
     friend class __bit_iterator<__bitset, true>;
-    friend class __bit_array<__bitset>;
+    friend struct __bit_array<__bitset>;
 
     __storage_type __first_[_N_words];
 
@@ -435,7 +435,7 @@
     friend class __bit_const_reference<__bitset>;
     friend class __bit_iterator<__bitset, false>;
     friend class __bit_iterator<__bitset, true>;
-    friend class __bit_array<__bitset>;
+    friend struct __bit_array<__bitset>;
 
     __storage_type __first_;