I have actually implemented it a few weeks ago. There is still an issue with it: in libdiskfs/file-exec.c and libnetfs/file-exec.c,  ‘fshelp_exec_reauth’ is called with a const parameter.

For instance, GNU Mach's include/device/device.defs declares

routine device_write(
                device          : device_t;
        sreplyport reply_port   : reply_port_t;
        in      mode            : dev_mode_t;
        in      recnum          : recnum_t;
        in      data            : io_buf_ptr_t;
        out     bytes_written   : int
        );

which results to the following device_write prototype:

kern_return_t device_write
(
        mach_port_t device,
        dev_mode_t mode,
        recnum_t recnum,
        io_buf_ptr_t data,
        mach_msg_type_number_t dataCnt,
        int *bytes_written
);

memory pointed to by data is provided by the client and not modified by the server, so in this case "const" should be output just before io_buf_ptr_t.

That fix makes a lot of sense and would drop a bunch of spurious warnings in the glibc compilation log.