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/no_exceptions_test.cpp

@@ -17,7 +17,7 @@ my_exception:
     std::exception
     {
     char const *
-    what() const throw()
+    what() const BOOST_NOEXCEPT_OR_NOTHROW
         {
         return "my_exception";
         }