#if !defined(__cpp_fold_expressions) || (__cpp_fold_expressions < 201603)
# define BOOST_NO_CXX17_FOLD_EXPRESSIONS
#endif
+#if !defined(__cpp_if_constexpr) || (__cpp_if_constexpr < 201606)
+# define BOOST_NO_CXX17_IF_CONSTEXPR
+#endif
// Turn on threading support for Solaris 12.
// Ticket #11972