https://bugs.gentoo.org/869401

Partial hunk from https://github.com/boostorg/container_hash/commit/4e11c855cb4c7813c75ff5a34f3d9e4fe7d800a0.

From: Peter Dimov <pdimov@gmail.com>
Date: Sat, 16 Oct 2021 16:55:27 +0300
Subject: [PATCH] Remove use of <functional>

--- a/boost/container_hash/hash.hpp
+++ b/boost/container_hash/hash.hpp
@@ -69,17 +68,12 @@ namespace boost
 {
     namespace hash_detail
     {
-#if defined(BOOST_NO_CXX98_FUNCTION_BASE)
         template <typename T>
         struct hash_base
         {
             typedef T argument_type;
             typedef std::size_t result_type;
         };
-#else
-        template <typename T>
-        struct hash_base : std::unary_function<T, std::size_t> {};
-#endif
 
         struct enable_hash_value { typedef std::size_t type; };