[libc++] Fix PR22922 - Allocator support for std::function does not know how to rebind.

Summary:
This patch changes std::function to use allocator_traits to rebind the allocator instead of allocator itself.

It also changes most of the tests to use `bare_allocator` where possible instead of `test_allocator`.

Reviewers: mclow.lists

Reviewed By: mclow.lists

Subscribers: cfe-commits

Differential Revision: http://reviews.llvm.org/D8391

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@232686 91177308-0d34-0410-b5e6-96231b3b80d8

test/std/utilities/function.objects/func.wrap/func.wrap.func/func.wrap.func.con/alloc.pass.cpp

@@ -16,10 +16,12 @@
 #include <functional>
 #include <cassert>
 
-#include "test_allocator.h"
+#include "min_allocator.h"
 
 int main()
 {
-    std::function<int(int)> f(std::allocator_arg, test_allocator<int>());
+    {
+    std::function<int(int)> f(std::allocator_arg, bare_allocator<int>());
     assert(!f);
+    }
 }