Function derive_unaligned_union 

pub(crate) fn derive_unaligned_union(
    ast: &DeriveInput,
    unn: &DataUnion,
    zerocopy_crate: &Path,
) -> Result<TokenStream, Error>

Like structs, a union is Unaligned if:

• repr(align) is no more than 1 and either
  • repr(C) or repr(transparent) and
    • all fields Unaligned
  • repr(packed)