Make endian_arithmetic's data member public when BOOST_ENDIAN_NO_CTORS is defined; add test

test/packed_arithmetic_test.cpp

@@ -0,0 +1,33 @@
+// Copyright 2020 Peter Dimov
+// Distributed under the Boost Software License, Version 1.0.
+// https://www.boost.org/LICENSE_1_0.txt
+
+#if !defined(__GNUC__)
+
+#include <boost/config/pragma_message.hpp>
+BOOST_PRAGMA_MESSAGE( "Skipping test because __GNUC__ is not defined" )
+int main() {}
+
+#else
+
+#define BOOST_ENDIAN_FORCE_PODNESS
+#define BOOST_ENDIAN_NO_CTORS
+#include <boost/endian/arithmetic.hpp>
+#include <boost/core/lightweight_test.hpp>
+
+using namespace boost::endian;
+
+struct X
+{
+    big_uint16_t a;
+    double b;
+    little_uint16_t c;
+} __attribute__((packed));
+
+int main()
+{
+    BOOST_TEST_EQ( sizeof( X ), 12 );
+    return boost::report_errors();
+}
+
+#endif