Fix LWG#2476: scoped_allocator_adaptor is not assignable

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@251253 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/include/scoped_allocator b/include/scoped_allocator
index cd4987a..9436dac 100644
--- a/include/scoped_allocator
+++ b/include/scoped_allocator
@@ -58,6 +58,8 @@
     template <class OuterA2>
         scoped_allocator_adaptor(const scoped_allocator_adaptor<OuterA2, InnerAllocs...>&& other) noexcept;
 
+    scoped_allocator_adaptor& operator=(const scoped_allocator_adaptor&) = default;
+    scoped_allocator_adaptor& operator=(scoped_allocator_adaptor&&) = default;
     ~scoped_allocator_adaptor();
 
     inner_allocator_type& inner_allocator() noexcept;
@@ -457,6 +459,8 @@
             scoped_allocator_adaptor<_OuterA2, _InnerAllocs...>&& __other) _NOEXCEPT
                 : base(_VSTD::move(__other)) {}
 
+    // scoped_allocator_adaptor& operator=(const scoped_allocator_adaptor&) = default;
+    // scoped_allocator_adaptor& operator=(scoped_allocator_adaptor&&) = default;
     // ~scoped_allocator_adaptor() = default;
 
     _LIBCPP_INLINE_VISIBILITY