MDEV-36427 - FTBFS with libxml2 2.14.0

Connect engine fails to build with libxml2 2.14.0.

Connect engine uses "#ifndef BASE_BUFFER_SIZE" to determine if libxml2 is
available. If libxml2 is unavailable it did redefine xmlElementType enum
of libxml/tree.h. The reasons for this redefinition is vague, most
probably some of these constants were used when connect was compiled with
MSXML, while libxml2 was disabled.

However BASE_BUFFER_SIZE constant was removed from libxml2 recently, as
a result connect fails to build due to xmlElementType constants
redefinition.

Use LIBXML2_SUPPORT instead of BASE_BUFFER_SIZE for libxml2 availability
check.

storage/connect/plgxml.h

@@ -5,7 +5,7 @@
 /******************************************************************/
 /*  Dual XML implementation base classes defines.                 */
 /******************************************************************/
-#if !defined(BASE_BUFFER_SIZE)
+#ifndef LIBXML2_SUPPORT
 enum ElementType {               // libxml2
      XML_ELEMENT_NODE       =  1,
      XML_ATTRIBUTE_NODE     =  2,
@@ -28,7 +28,7 @@ enum ElementType {               // libxml2
      XML_XINCLUDE_START     = 19,
      XML_XINCLUDE_END       = 20,
      XML_DOCB_DOCUMENT_NODE = 21};
-#endif   // !BASE_BUFFER_SIZE
+#endif
 
 //#if !defined(NODE_TYPE_LIST)
 #ifdef NOT_USED

storage/connect/tabxml.cpp

@@ -26,6 +26,9 @@
 #include <netinet/in.h>
 #include <unistd.h>
 //#include <ctype.h>
+#ifdef LIBXML2_SUPPORT
+#include <libxml/tree.h>
+#endif
 #include "osutil.h"
 #define _O_RDONLY O_RDONLY
 #endif  // !_WIN32