added deprecation warning for POCO_WIN32_UTF8

Foundation/include/Poco/Platform_WIN32.h

@@ -172,6 +172,11 @@
 #endif
 
 
+#if !defined(POCO_WIN32_UTF8)
+	#warning Compiling POCO on Windows without #define POCO_WIN32_UTF8 is deprecated.
+#endif
+
+
 // Turn off some annoying warnings
 #if defined(_MSC_VER)
 	#pragma warning(disable:4018)	// signed/unsigned comparison