build: Avoid `BOOST_NO_CXX98_FUNCTION_BASE` macro redefinition

configure.ac

@@ -1479,9 +1479,11 @@ if test "$use_boost" = "yes"; then
   BOOST_CPPFLAGS="$BOOST_CPPFLAGS -DBOOST_MULTI_INDEX_DISABLE_SERIALIZATION"
 
   dnl Prevent use of std::unary_function, which was removed in C++17,
-  dnl and will generate warnings with newer compilers.
-  dnl See: https://github.com/boostorg/container_hash/issues/22.
-  BOOST_CPPFLAGS="$BOOST_CPPFLAGS -DBOOST_NO_CXX98_FUNCTION_BASE"
+  dnl and will generate warnings with newer compilers for Boost
+  dnl older than 1.80.
+  dnl See: https://github.com/boostorg/config/pull/430.
+  AX_CHECK_PREPROC_FLAG([-DBOOST_NO_CXX98_FUNCTION_BASE], [BOOST_CPPFLAGS="$BOOST_CPPFLAGS -DBOOST_NO_CXX98_FUNCTION_BASE"], [], [$CXXFLAG_WERROR],
+                        [AC_LANG_PROGRAM([[#include <boost/config.hpp>]])])
 
   if test "$enable_debug" = "yes" || test "$enable_fuzz" = "yes"; then
     BOOST_CPPFLAGS="$BOOST_CPPFLAGS -DBOOST_MULTI_INDEX_ENABLE_SAFE_MODE"