[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