Bug#37387318 Add standalone xxhash library

Post-push fix: update Copyright notice.

Change-Id: I85272c64686479e6e069dff6358b350d67e1627f

Author: Tor Didriksen

extra/xxhash/my_xxhash.h

@@ -1,26 +1,26 @@
-/*
-  Copyright (c) 2016, 2025, Oracle and/or its affiliates.
-
-  This program is free software; you can redistribute it and/or modify
-  it under the terms of the GNU General Public License, version 2.0,
-  as published by the Free Software Foundation.
-
-  This program is also distributed with certain software (including
-  but not limited to OpenSSL) that is licensed under separate terms,
-  as designated in a particular file or component or in included license
-  documentation.  The authors of MySQL hereby grant you an additional
-  permission to link the program and your derivative works with the
-  separately licensed software that they have included with MySQL.
-
-  This program is distributed in the hope that it will be useful,
-  but WITHOUT ANY WARRANTY; without even the implied warranty of
-  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
-  GNU General Public License, version 2.0, for more details.
-
-  You should have received a copy of the GNU General Public License
-  along with this program; if not, write to the Free Software
-  Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301  USA
-*/
+/* Copyright (c) 2016, 2025, Oracle and/or its affiliates.
+
+   This program is free software; you can redistribute it and/or modify
+   it under the terms of the GNU General Public License, version 2.0,
+   as published by the Free Software Foundation.
+
+   This program is designed to work with certain software (including
+   but not limited to OpenSSL) that is licensed under separate terms,
+   as designated in a particular file or component or in included license
+   documentation.  The authors of MySQL hereby grant you an additional
+   permission to link the program and your derivative works with the
+   separately licensed software that they have either included with
+   the program or referenced in the documentation.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License, version 2.0, for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program; if not, write to the Free Software
+   Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301  USA */
+
 
 # pragma once