Disable -Wconversion for GCC 5 in test_hash_value.cpp

test/test_hash_value.cpp

@@ -2,6 +2,10 @@
 // Distributed under the Boost Software License, Version 1.0.
 // https://www.boost.org/LICENSE_1_0.txt
 
+#if defined(__GNUC__) && __GNUC__ == 5
+# pragma GCC diagnostic ignored "-Wconversion"
+#endif
+
 #include <boost/uuid/uuid.hpp>
 #include <boost/core/lightweight_test.hpp>
 #include <unordered_set>