Function guile_sys::scm_set_port_get_natural_buffer_sizes

pub unsafe extern "C" fn scm_set_port_get_natural_buffer_sizes(
    ptob: *mut scm_t_port_type, 
    get_natural_buffer_sizes: Option<unsafe extern "C" fn(arg1: SCM, arg2: *mut usize, arg3: *mut usize)>
)