Rollup merge of #129684 - Strophox:miri-pass-pointer-to-ffi, r=RalfJung

Enable Miri to pass pointers through FFI

Following https://github.com/rust-lang/rust/pull/126787, the purpose of this PR is to now enable Miri to execute native calls that make use of pointers.

> <details>
>
> <summary> Simple example </summary>
>
> ```rust
> extern "C" {
>     fn ptr_printer(ptr: *mut i32);
> }
>
> fn main() {
>     let ptr = &mut 42 as *mut i32;
>     unsafe {
>         ptr_printer(ptr);
>     }
> }
> ```
> ```c
> void ptr_printer(int *ptr) {
>   printf("printing pointer dereference from C: %d\n", *ptr);
> }
> ```
> should now show `printing pointer dereference from C: 42`.
>
> </details>

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``

compiler/rustc_middle/src/mir/interpret/allocation.rs

@@ -358,10 +358,11 @@ impl Allocation {
     pub fn adjust_from_tcx<Prov: Provenance, Bytes: AllocBytes, Err>(
         &self,
         cx: &impl HasDataLayout,
+        mut alloc_bytes: impl FnMut(&[u8], Align) -> Result<Bytes, Err>,
         mut adjust_ptr: impl FnMut(Pointer<CtfeProvenance>) -> Result<Pointer<Prov>, Err>,
     ) -> Result<Allocation<Prov, (), Bytes>, Err> {
         // Copy the data.
-        let mut bytes = Bytes::from_bytes(Cow::Borrowed(&*self.bytes), self.align);
+        let mut bytes = alloc_bytes(&*self.bytes, self.align)?;
         // Adjust provenance of pointers stored in this allocation.
         let mut new_provenance = Vec::with_capacity(self.provenance.ptrs().len());
         let ptr_size = cx.data_layout().pointer_size.bytes_usize();