Based on Arnaud Patard patch for mysql 5.5.8
===================================================================
--- mysql-5.5.16/sql-common/client_plugin.c	2011-09-30 13:09:10.709154000 +0200
+++ mysql-5.5.16/sql-common/client_plugin_new.c	2011-09-30 13:11:53.753154000 +0200
@@ -228,6 +228,7 @@
 {
   MYSQL mysql;
   struct st_mysql_client_plugin **builtin;
+  va_list dummy;
 
   if (initialized)
     return 0;
@@ -244,7 +245,7 @@
   pthread_mutex_lock(&LOCK_load_client_plugin);
 
   for (builtin= mysql_client_builtins; *builtin; builtin++)
-    add_plugin(&mysql, *builtin, 0, 0, 0);
+    add_plugin(&mysql, *builtin, 0, 0, dummy);
 
   pthread_mutex_unlock(&LOCK_load_client_plugin);
 
@@ -288,6 +289,7 @@
 mysql_client_register_plugin(MYSQL *mysql,
                              struct st_mysql_client_plugin *plugin)
 {
+  va_list dummy;
   if (is_not_initialized(mysql, plugin->name))
     return NULL;
 
@@ -302,7 +304,7 @@
     plugin= NULL;
   }
   else
-    plugin= add_plugin(mysql, plugin, 0, 0, 0);
+    plugin= add_plugin(mysql, plugin, 0, 0, dummy);
 
   pthread_mutex_unlock(&LOCK_load_client_plugin);
   return plugin;