Replaced throw() with BOOST_NOEXCEPT_OR_NOTHROW

With throw(), Visual Studio 2017 emitted a warning "C26439 SPECIAL_NOEXCEPT". Reproducible at least if code analysis was set to level: "Microsoft Native Recommended Rules".

https://docs.microsoft.com/en-us/visualstudio/code-quality/c26439?view=vs-2017

test/cloning_test.cpp

@@ -73,7 +73,7 @@ derives_std_boost_exception:
         {
         }
 
-    char const * what() const throw()
+    char const * what() const BOOST_NOEXCEPT_OR_NOTHROW
         {
         return wh_;
         }