In many places, there was an #ifdef/#else block that selected one of two implmentations of rebind_alloc based on whether or not we had template aliases. Create a helper struct to encapsulate that bit of logic, and replace all the ifdefs with uses of that struct. No functionality change intented.

llvm-svn: 234296
Cr-Mirrored-From: sso://chromium.googlesource.com/_direct/external/github.com/llvm/llvm-project
Cr-Mirrored-Commit: 1f508014df7da33d684a5c0cb3c059a675a0aacf
diff --git a/include/vector b/include/vector
index efe21e1..48e970a 100644
--- a/include/vector
+++ b/include/vector
@@ -2125,13 +2125,7 @@
     typedef _VSTD::reverse_iterator<const_iterator>   const_reverse_iterator;
 
 private:
-    typedef typename __alloc_traits::template
-#ifndef _LIBCPP_HAS_NO_TEMPLATE_ALIASES
-                rebind_alloc<__storage_type>
-#else
-                rebind_alloc<__storage_type>::other
-#endif
-                                                     __storage_allocator;
+    typedef typename __rebind_alloc_helper<__alloc_traits, __storage_type>::type __storage_allocator;
     typedef allocator_traits<__storage_allocator>    __storage_traits;
     typedef typename __storage_traits::pointer       __storage_pointer;
     typedef typename __storage_traits::const_pointer __const_storage_pointer;