Problem: The fix for bug #23607230 used xxhash symbols from liblz4,
but even though the xxhash symbols are exported by liblz4, the header
file is not part of the API, so compilation fails when building with
WITH_LZ4=system.

Fix: Build xxhash separately from liblz4 so that it's available both
when using system and bundled lz4 libraries.
---
 extra/lz4/my_xxhash.h        | 27 +++++++++++++++++++++++++++
 libmysqld/CMakeLists.txt     |  6 ++++++
 sql/CMakeLists.txt           |  6 ++++++
 sql/rpl_write_set_handler.cc |  4 ++--
 4 files changed, 41 insertions(+), 2 deletions(-)
 create mode 100644 extra/lz4/my_xxhash.h

diff --git a/extra/lz4/my_xxhash.h b/extra/lz4/my_xxhash.h
new file mode 100644
index 0000000..699c1b5
--- /dev/null
+++ b/extra/lz4/my_xxhash.h
@@ -0,0 +1,27 @@
+#ifndef MY_XXHASH_H_INCLUDED
+#define MY_XXHASH_H_INCLUDED
+
+/*
+  Copyright (c) 2016, Oracle and/or its affiliates. All rights reserved.
+
+  This program is free software; you can redistribute it and/or modify
+  it under the terms of the GNU General Public License as published by
+  the Free Software Foundation; version 2 of the License.
+
+  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 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,
+  51 Franklin Street, Suite 500, Boston, MA 02110-1335 USA
+*/
+
+// Define a namespace prefix to all xxhash functions. This is done to
+// avoid conflict with xxhash symbols in liblz4.
+#define XXH_NAMESPACE MY_
+
+#include "xxhash.h"
+
+#endif // MY_XXHASH_H_INCLUDED
diff --git a/libmysqld/CMakeLists.txt b/libmysqld/CMakeLists.txt
index cb188ec..0093f2e 100644
--- a/libmysqld/CMakeLists.txt
+++ b/libmysqld/CMakeLists.txt
@@ -62,6 +62,7 @@ SET(SQL_EMBEDDED_SOURCES
   libmysqld.c
   ${GEN_SOURCES}
   ${GEN_YACC_SOURCES}
+  ../extra/lz4/xxhash.c
   ../client/get_password.c
   ../libmysql/errmsg.c
   ../libmysql/libmysql.c
@@ -118,6 +119,11 @@ ADD_COMPILE_FLAGS(
   COMPILE_FLAGS -I${BOOST_PATCHES_DIR} -I${BOOST_INCLUDE_DIR}
 )
 
+ADD_COMPILE_FLAGS(
+  ../extra/lz4/xxhash.c
+  COMPILE_FLAGS -DXXH_NAMESPACE=MY_
+)
+
 # Fixes "C1128: number of sections exceeded object file format limit" in MSVC /MD
 # The flag /bigobj is not added if the build is not /MD
 IF(WIN32 AND CMAKE_SIZEOF_VOID_P MATCHES 8)
diff --git a/sql/CMakeLists.txt b/sql/CMakeLists.txt
index 50352b1..ea42ff5 100644
--- a/sql/CMakeLists.txt
+++ b/sql/CMakeLists.txt
@@ -254,6 +254,7 @@ SET(SQL_SOURCE
   ${GEN_DIGEST_SOURCES}
   ${CONF_SOURCES}
   ${SQL_SHARED_SOURCES}
+  ../extra/lz4/xxhash.c
   ../libmysql/errmsg.c
   ../sql-common/client.c
   ../sql-common/client_plugin.c
@@ -314,6 +315,11 @@ ADD_COMPILE_FLAGS(
   COMPILE_FLAGS -I${BOOST_PATCHES_DIR} -I${BOOST_INCLUDE_DIR}
 )
 
+ADD_COMPILE_FLAGS(
+  ../extra/lz4/xxhash.c
+  COMPILE_FLAGS -DXXH_NAMESPACE=MY_
+)
+
 # Fixes "C1128: number of sections exceeded object file format limit" in MSVC /MD
 # The flag /bigobj is not added if the build is not WINDOWS_RUNTIME_MD (/MD)
 IF(WINDOWS_RUNTIME_MD AND CMAKE_SIZEOF_VOID_P MATCHES 8)
diff --git a/sql/rpl_write_set_handler.cc b/sql/rpl_write_set_handler.cc
index 3897321..c7e778e 100644
--- a/sql/rpl_write_set_handler.cc
+++ b/sql/rpl_write_set_handler.cc
@@ -23,7 +23,7 @@
 #include "table.h"         // TABLE
 
 #include "my_murmur3.h"    // murmur3_32
-#include "xxhash.h"        // xxHash
+#include "../extra/lz4/my_xxhash.h" // xxHash
 
 #include <map>
 #include <string>
@@ -61,7 +61,7 @@ template <class type> uint64 calc_hash(ulong algorithm, type T)
   if(algorithm == HASH_ALGORITHM_MURMUR32)
     return (murmur3_32((const uchar*)T, strlen(T), 0));
   else
-    return (XXH64((const uchar*)T, strlen(T), 0));
+    return (MY_XXH64((const uchar*)T, strlen(T), 0));
 }
 
 /**
-- 
2.1.0