X3.Examples: tuple: Do not run on unsupported compilers

example/x3/Jamfile

@@ -4,6 +4,8 @@
 #   Distributed under the Boost Software License, Version 1.0. (See accompanying
 #   file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
 #==============================================================================
+import config : requires ;
+
 project spirit-x3-example
     : requirements
         <include>.
@@ -62,4 +64,4 @@ exe x3_calc9 :
     calc/calc9/main.cpp
 ;
 
-exe x3_tuple : attributes/tuple.cpp ;
+exe x3_tuple : attributes/tuple.cpp : [ requires cxx17_structured_bindings ] ;

example/x3/attributes/tuple.cpp

@@ -1,4 +1,3 @@
-
 /*=============================================================================
     Copyright (c) 2019 Tom Tan
 
@@ -47,4 +46,4 @@ int main()
   std::cout << "length = " << len << '\n'
             << "id = " << id << '\n'
             << "revision =" << rev;
-}
+}