fn add_to_ancillary_data<T>(
buffer: &mut [u8],
length: &mut usize,
source: &[T],
cmsg_level: c_int,
cmsg_type: c_int,
) -> boolAvailable on non-Hermit and (Unix) and not ((WebAssembly and non-WASI, or Fortanix and SGX)) and (Android or Linux or Cygwin) only.