diff -ruN boost-1_69_0/boost/system/detail/system_category_win32.hpp boost-1_69_0-new/boost/system/detail/system_category_win32.hpp
--- boost-1_69_0/boost/system/detail/system_category_win32.hpp	2018-12-05 12:58:23.000000000 -0700
+++ boost-1_69_0-new/boost/system/detail/system_category_win32.hpp	2018-12-22 10:08:47.349000800 -0700
@@ -26,7 +26,7 @@
 namespace detail
 {
 
-#if ( defined(_MSC_VER) && _MSC_VER < 1900 ) || ( defined(__MINGW32__) && !defined(__MINGW64_VERSION_MAJOR) )
+#if ( defined(_MSC_VER) && _MSC_VER < 1900 ) || ( defined(__MINGW32__) && !defined(__MINGW64_VERSION_MAJOR) || (defined(_WIN32) && defined(__clang__)))
 
 inline char const * unknown_message_win32( int ev, char * buffer, std::size_t len )
 {