$OpenBSD: patch-configure,v 1.3 2017/12/26 19:18:57 rsadowski Exp $

Index: configure
--- configure.orig
+++ configure
@@ -18015,6 +18015,7 @@ else
 do :
   ac_fn_cxx_check_header_mongrel "$LINENO" "boost/spirit.hpp" "ac_cv_header_boost_spirit_hpp" "$ac_includes_default"
 if test "x$ac_cv_header_boost_spirit_hpp" = xyes; then :
+  LIBS="-lboost_system  $LIBS"
   cat >>confdefs.h <<_ACEOF
 #define HAVE_BOOST_SPIRIT_HPP 1
 _ACEOF
