Enable Miri to pass pointers through FFI

[Strophox]

Following #126787, the purpose of this PR is to now enable Miri to execute native calls that make use of pointers.

Simple example

extern "C" {
    fn ptr_printer(ptr: *mut i32);
}

fn main() {
    let ptr = &mut 42 as *mut i32;
    unsafe {
        ptr_printer(ptr);
    }
}

void ptr_printer(int *ptr) {
  printf("printing pointer dereference from C: %d\n", *ptr);
}

should now show printing pointer dereference from C: 42.

Note that this PR does not yet implement any logic involved in updating Miri's "analysis" state (byte initialization, provenance) upon such a native call.

r? @RalfJung

[rustbot]

Some changes occurred to the CTFE / Miri engine

cc @rust-lang/miri

Some changes occurred to the CTFE / Miri engine

cc @rust-lang/miri

The Miri subtree was changed

cc @rust-lang/miri

[Strophox]

Oh. Well that didn't work yet.

[RalfJung]

🎉

[Strophox]

(I might quickly try to enhance+refactor the C pointer FFI tests in Miri now.)

[RalfJung]

Looks good overall, thanks! Just got some nits regarding the tests.

[RalfJung]

Please squash the commits, then we can land this. :-)

[RalfJung]

Great, congrats on getting this finished!

@bors r+

[bors]

📌 Commit 7fde02e has been approved by RalfJung

It is now in the queue for this repository.