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/__tree b/include/__tree
index 77bf081..588f438 100644
--- a/include/__tree
+++ b/include/__tree
@@ -802,13 +802,7 @@
 
     typedef __tree_node<value_type, __void_pointer> __node;
     typedef __tree_node_base<__void_pointer>        __node_base;
-    typedef typename __alloc_traits::template
-#ifndef _LIBCPP_HAS_NO_TEMPLATE_ALIASES
-            rebind_alloc<__node>
-#else
-            rebind_alloc<__node>::other
-#endif
-                                                     __node_allocator;
+    typedef typename __rebind_alloc_helper<__alloc_traits, __node>::type __node_allocator;
     typedef allocator_traits<__node_allocator>       __node_traits;
     typedef typename __node_traits::pointer          __node_pointer;
     typedef typename __node_traits::pointer          __node_const_pointer;