Disable codecvt warning on Windows.

The comment has more information about why we need this.

Signed-off-by: Chris Lalancette <clalancette@openrobotics.org>

rosidl_runtime_cpp/include/rosidl_runtime_cpp/traits.hpp

@@ -20,6 +20,14 @@
 #include <string>
 #include <type_traits>
 
+// In C++17 mode, MSVC 2019 warns that
+// std::wstring_convert<std::codecvt_utf8_utf16<char16_t>, char16_t> is deprecated.
+// However, it appears that there is no cross-platform replacement for it at present.
+// Thus, we follow the warning advice and disable this warning for Windows.
+#ifdef _WIN32
+#define _SILENCE_CXX17_CODECVT_HEADER_DEPRECATION_WARNING
+#endif
+
 namespace rosidl_generator_traits
 {