SFINAE __bit_iterator such that it will only get instantiated with a container that has the nested type __storage_type.  This prevents accidental instantiation such as in http://llvm.org/bugs/show_bug.cgi?id=12755.  This fixes http://llvm.org/bugs/show_bug.cgi?id=12755.

llvm-svn: 156308
Cr-Mirrored-From: sso://chromium.googlesource.com/_direct/external/github.com/llvm/llvm-project
Cr-Mirrored-Commit: 0ae9efeb1a14a665a0f5d6819e25a83cc6ea348a
diff --git a/include/vector b/include/vector
index 61f0aef..0d5b6b8 100644
--- a/include/vector
+++ b/include/vector
@@ -1970,6 +1970,7 @@
     typedef allocator_traits<allocator_type>         __alloc_traits;
     typedef typename __alloc_traits::size_type       size_type;
     typedef typename __alloc_traits::difference_type difference_type;
+    typedef size_type __storage_type;
     typedef __bit_iterator<vector, false>            pointer;
     typedef __bit_iterator<vector, true>             const_pointer;
 #ifdef _LIBCPP_DEBUG
@@ -1991,7 +1992,6 @@
     typedef _VSTD::reverse_iterator<const_iterator>   const_reverse_iterator;
 
 private:
-    typedef size_type __storage_type;
     typedef typename __alloc_traits::template
 #ifndef _LIBCPP_HAS_NO_TEMPLATE_ALIASES
                 rebind_alloc<__storage_type>