Fix thread variable linking errors

Define mysql_thread___eventslog_file_rotation_mode and mysql_thread___auditlog_file_rotation_mode
directly in MySQL_Thread.cpp to resolve undefined reference linker errors.

The variables were declared but not defined, causing linking failures during compilation.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <[email protected]>

Author: takaidohigasi

include/proxysql_structs.h

@@ -1318,12 +1318,10 @@ __thread int mysql_thread___eventslog_buffer_max_query_length;
 __thread int mysql_thread___eventslog_default_log;
 __thread int mysql_thread___eventslog_format;
 __thread int mysql_thread___eventslog_stmt_parameters;
-__thread char * mysql_thread___eventslog_file_rotation_mode;
 
 /* variables used by audit log */
 __thread char * mysql_thread___auditlog_filename;
 __thread int mysql_thread___auditlog_filesize;
-__thread char * mysql_thread___auditlog_file_rotation_mode;
 
 /* variables used by the monitoring module */
 __thread int mysql_thread___monitor_enabled;

lib/MySQL_Thread.cpp

@@ -197,6 +197,10 @@ extern "C" {
 
 __thread unsigned int __thread_MySQL_Thread_Variables_version;
 
+// Thread variables for rotation mode functionality
+__thread char * mysql_thread___eventslog_file_rotation_mode;
+__thread char * mysql_thread___auditlog_file_rotation_mode;
+
 volatile static unsigned int __global_MySQL_Thread_Variables_version;