fix max_size.pass.cpp

Author: vinay-deshmukh

libcxx/include/__tree

@@ -957,7 +957,7 @@ private:
   _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 const __iter_pointer& __begin_node() const _NOEXCEPT { return __begin_node_; }
 
 public:
-  _LIBCPP_HIDE_FROM_ABI allocator_type __alloc() const _NOEXCEPT { return allocator_type(__node_alloc()); }
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 allocator_type __alloc() const _NOEXCEPT { return allocator_type(__node_alloc()); }
 
 private:
   _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 size_type& size() _NOEXCEPT { return __size_; }