Opaque types don't include `!Send`, `!Sync`, `!Pin`

We have a pointer type to an opaque type in our FFI project.

Bindgen generates this definition for the opaque type:

#[repr(C)]
#[derive(Debug, Copy, Clone)]
pub struct SEXPREC {
    _unused: [u8; 0],
}

But then I was reading https://stackoverflow.com/questions/38315383/whats-the-rust-idiom-to-define-a-field-pointing-to-a-c-opaque-pointer, and https://doc.rust-lang.org/nomicon/ffi.html#representing-opaque-structs,
which says that the definition of the above should really be:

#[repr(C)]
pub struct SEXPREC {
    _data: [u8; 0],
    _marker:
        core::marker::PhantomData<(*mut u8, core::marker::PhantomPinned)>,
}

Is this something I should replace the bindgen-version with this?

Lastly, I merely have these in the C-headers:

typedef struct SEXPREC s_object;

with no definition of s_object, and I'm quite certain this is intended behavior.

Start by examining bindgen's generation of opaque Rust structs from the incomplete C declaration typedef struct SEXPREC s_object;, then compare the generated type's auto-trait behavior with the Rust Nomicon guidance linked in the issue. Done means determining and documenting whether the generated opaque type should include !Send, !Sync, and !Pin, with regression coverage for the intended behavior.