Do not define _SCL_SECURE_NO_WARNINGS or _CRT_SECURE_NO_WARNINGS if already defined (such as on the command line), plus related cleanups.

test/benchmark.cpp

@@ -5,8 +5,13 @@
 //  Distributed under the Boost Software License, Version 1.0.
 //  http://www.boost.org/LICENSE_1_0.txt
 
-#define _CRT_SECURE_NO_WARNINGS
-#define _SCL_SECURE_NO_WARNINGS
+#ifndef _SCL_SECURE_NO_WARNINGS
+# define _SCL_SECURE_NO_WARNINGS
+#endif
+
+#ifndef _CRT_SECURE_NO_WARNINGS
+# define _CRT_SECURE_NO_WARNINGS
+#endif
 
 #include <cstdlib>
 #include <boost/endian/conversion.hpp>