Add deduction guides to shared_ptr and weak_ptr. Fixes #73.

test/wp_guides_test.cpp

@@ -0,0 +1,24 @@
+// Copyright 2020 Peter Dimov
+// Distributed under the Boost Software License, Version 1.0.
+// https://www.boost.org/LICENSE_1_0.txt
+
+#if defined(__cpp_deduction_guides)
+
+#include <boost/shared_ptr.hpp>
+#include <boost/weak_ptr.hpp>
+
+int main()
+{
+    boost::shared_ptr<int> p1( new int );
+    boost::weak_ptr p2( p1 );
+}
+
+#else
+
+#include <boost/config/pragma_message.hpp>
+
+BOOST_PRAGMA_MESSAGE( "Skipping test because __cpp_deduction_guides is not defined" )
+
+int main() {}
+
+#endif