MDEV-3824 - xtradb file rename fails on Windows, if new name already exists.

Changed implementation os_file_rename() on Windows  such as it does not fail if destination file already exists. Now MoveFileEx() with MOVEFILE_REPLACE_EXISTING flag is used, instead of prior MoveFile().
This fixed implementation is better compatible with rename() on POSIX systems.

storage/xtradb/os/os0file.c

@@ -1870,7 +1870,7 @@ os_file_rename_func(
 #ifdef __WIN__
 	BOOL	ret;
 
-	ret = MoveFile((LPCTSTR)oldpath, (LPCTSTR)newpath);
+	ret = MoveFileEx((LPCTSTR)oldpath, (LPCTSTR)newpath, MOVEFILE_REPLACE_EXISTING);
 
 	if (ret) {
 		return(TRUE);