... if they use arbitrary enum discriminant. Code like

```rust
enum Enum {
    Foo = 1,
    Bar(),
    Baz{}
}
```

seems to be unintentionally allowed so we couldn't disallow them now,
but we could disallow them if arbitrary enum discriminant is used before
1.56 hits stable.

Disallow non-c-like but "fieldless" ADTs from being casted to integer if they use arbitrary enum discriminant

Code like

```rust
#[repr(u8)]
enum Enum {
    Foo /* = 0 */,
    Bar(),
    Baz{}
}

let x = Enum::Bar() as u8;
```

seems to be unintentionally allowed so we couldn't disallow them now ~~, but we could disallow them if arbitrary enum discriminant is used before 1.56 hits stable~~ (stabilization was reverted).

Related: rust-lang#88621

`@rustbot` label +T-lang

…nkov

Issue 90702 fix: Stop treating some crate loading failures as fatal errors

Surface mulitple `extern crate` resolution errors at a time.

This is achieved by creating a dummy crate, instead of aborting directly after the resolution error. The `ExternCrateError` has been added to allow propagating the resolution error from `rustc_metadata` crate to the `rustc_resolve` with a minimal public surface. The `import_extern_crate` function is a block that was factored out from `build_reduced_graph_for_item` for better organization. The only added functionality made to it where the added error handling in the `process_extern_crate` call. The remaining bits in this function are the same as before.

Resolves rust-lang#90702

r? `@petrochenkov`

…roalbini

Bump stage0 compiler

r? `@pietroalbini` (or anyone else)

…nkov

Enable svh tests on msvc

These tests were ignored for msvc in rust-lang#30778 because of additional notes that were being added for some reason. I'm fairly confident this has been fixed in the intervening years so lets try re-enabling these tests.

Fixes rust-lang#31306