Deprecated boost/iterator.hpp, emit warnings on inclusion.

The header defines boost::iterator template, which is an alias for
std::iterator, which is itself deprecated since C++17.

Updated test to avoid testing the definition in C++17 onwards
to avoid failures due to deprecation warnings from libc++-13.

test/iterator_test.cpp

@@ -8,8 +8,15 @@
 // http://www.boost.org/LICENSE_1_0.txt
 //
 
+#define BOOST_ALLOW_DEPRECATED_HEADERS
 #define _SILENCE_CXX17_ITERATOR_BASE_CLASS_DEPRECATION_WARNING
 
+#include <boost/config.hpp>
+
+// std::iterator template is deprecated in C++17. Some standard libraries emit warnings
+// that cannot be easily suppressed, so disable the tests in C++17 onwards.
+#if BOOST_CXX_VERSION < 201703
+
 #include <boost/iterator.hpp>
 #include <boost/core/is_same.hpp>
 #include <boost/core/lightweight_test_trait.hpp>
@@ -69,3 +76,11 @@ int main()
 
     return boost::report_errors();
 }
+
+#else // BOOST_CXX_VERSION < 201703
+
+int main()
+{
+}
+
+#endif // BOOST_CXX_VERSION < 201703