build: Avoid BOOST_NO_CXX98_FUNCTION_BASE macro redefinition (#2715)

configure.ac

@@ -1061,10 +1061,12 @@ fi
 
 if test x$use_boost = xyes; then
 
-  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="$BOOST_CPPFLAGS -DBOOST_NO_CXX98_FUNCTION_BASE"
+  dnl Prevent use of std::unary_function, which was removed in C++17,
+  dnl and will generate warnings with newer compilers for Boost
+  dnl older than 1.80.
+  dnl See: https://github.com/boostorg/config/pull/430.
+  AX_CHECK_PREPROC_FLAG([-DBOOST_NO_CXX98_FUNCTION_BASE], [BOOST_CPPFLAGS="$BOOST_CPPFLAGS -DBOOST_NO_CXX98_FUNCTION_BASE"], [], [$CXXFLAG_WERROR],
+                        [AC_LANG_PROGRAM([[#include <boost/config.hpp>]])])
 
   BOOST_LIBS="$BOOST_LDFLAGS $BOOST_SYSTEM_LIB $BOOST_FILESYSTEM_LIB"
   LIBS="$BOOST_LIBS $LIBS"