Sync from upstream.

test/variant_json_value_from.cpp

@@ -2,6 +2,12 @@
 // Distributed under the Boost Software License, Version 1.0.
 // https://www.boost.org/LICENSE_1_0.txt
 
+#include <boost/config.hpp>
+
+#if defined(BOOST_GCC) && BOOST_GCC < 50000
+# define BOOST_ALLOW_DEPRECATED
+#endif
+
 #include <boost/variant2/variant.hpp>
 #include <boost/json/value_from.hpp>
 #include <boost/json/serialize.hpp>

test/variant_json_value_to.cpp

@@ -2,6 +2,12 @@
 // Distributed under the Boost Software License, Version 1.0.
 // https://www.boost.org/LICENSE_1_0.txt
 
+#include <boost/config.hpp>
+
+#if defined(BOOST_GCC) && BOOST_GCC < 50000
+# define BOOST_ALLOW_DEPRECATED
+#endif
+
 #include <boost/variant2/variant.hpp>
 #include <boost/json/value_to.hpp>
 #include <boost/json/serialize.hpp>