…petrochenkov

Delegation: allow foreign fns `reuse`

In example:
```rust
unsafe extern "C" {
    fn foo();
}

reuse foo as bar;
```

Desugaring before:

```rust
fn bar() {
    foo()
    //~^ ERROR call to unsafe function `foo` is unsafe and requires unsafe function or block
}
```

after:

```rust
unsafe extern "C" fn bar() {
    foo()
}
```

Fixes rust-lang#127412

r? `@petrochenkov`

…iaskrgr

Rollup of 8 pull requests

Successful merges:

 - rust-lang#138126 (Add an opt-out in pretty printing for RTN rendering)
 - rust-lang#138399 (Delegation: allow foreign fns `reuse`)
 - rust-lang#138406 (Update mdbook to 0.4.47)
 - rust-lang#138417 (minor interpreter cleanups)
 - rust-lang#138420 (Adapt to LLVM dropping CfiFunctionIndex::begin()/end())
 - rust-lang#138423 (Don't emit error within cast function, propagate it as a `CastError`)
 - rust-lang#138425 (Remove `feature = "hash_raw_entry"`)
 - rust-lang#138427 (Fix RISC-V VxWorks LLVM target triples)

r? `@ghost`
`@rustbot` modify labels: rollup

Rollup merge of rust-lang#138399 - Bryanskiy:delegation-extern-fn, r=petrochenkov

Delegation: allow foreign fns `reuse`

In example:
```rust
unsafe extern "C" {
    fn foo();
}

reuse foo as bar;
```

Desugaring before:

```rust
fn bar() {
    foo()
    //~^ ERROR call to unsafe function `foo` is unsafe and requires unsafe function or block
}
```

after:

```rust
unsafe extern "C" fn bar() {
    foo()
}
```

Fixes rust-lang#127412

r? `@petrochenkov`