MDEV-12244: C API header file contains C++ comment for COM_BINLOG_DUMP_GTID

fixed C++ comment in C code

include/mysql_com.h

@@ -111,7 +111,7 @@ enum enum_server_command
   COM_TABLE_DUMP, COM_CONNECT_OUT, COM_REGISTER_SLAVE,
   COM_STMT_PREPARE, COM_STMT_EXECUTE, COM_STMT_SEND_LONG_DATA, COM_STMT_CLOSE,
   COM_STMT_RESET, COM_SET_OPTION, COM_STMT_FETCH, COM_DAEMON,
-  COM_UNIMPLEMENTED, // COM_BINLOG_DUMP_GTID in MySQL
+  COM_UNIMPLEMENTED, /* COM_BINLOG_DUMP_GTID in MySQL */
   COM_RESET_CONNECTION,
   /* don't forget to update const char *command_name[] in sql_parse.cc */
   COM_MDB_GAP_BEG,