Define strncpyW to ensure that users know why it is not present.

include/wine/unicode.h

@@ -191,6 +191,9 @@ static inline WCHAR *strcpyW( WCHAR *dst, const WCHAR *src )
     return dst;
 }
 
+/* strncpy doesn't do what you think, don't use it */
+#define strncpyW(d,s,n) error do_not_use_strncpyW_use_lstrcpynW_or_memcpy_instead
+
 static inline int strcmpW( const WCHAR *str1, const WCHAR *str2 )
 {
     while (*str1 && (*str1 == *str2)) { str1++; str2++; }