Bug#21205695 DROP TABLE MAY CAUSE SLAVES TO BREAK

Correct fix. Generate the query in the client charset,
not in the system one.

sql/sql_table.cc

@@ -2092,7 +2092,7 @@ int mysql_rm_table_no_locks(THD *thd, TABLE_LIST *tables, bool if_exists,
       const char *comment_start;
       uint32 comment_len;
 
-      built_query.set_charset(system_charset_info);
+      built_query.set_charset(thd->charset());
       if (if_exists)
         built_query.append("DROP TABLE IF EXISTS ");
       else