…errors

MIR printing: print the path of uneval'd const

Currently it just prints `const _` which makes it impossible to say which constant is being referred to.

Also refer to promoteds in a consistent way; previously MIR printing would do
```
promoted[0] in C1: &Option<Cell<i32>> = {
    // ...
}
```
Now that should be
```
const C1::promoted[0]: &Option<Cell<i32>> = {
    // ...
}
```

We don't seem to have a test for that so I tried it by hand, it seems to work:
```
const main::promoted[12]: &[&str; 3] = {
    let mut _0: &[&str; 3];
    let mut _1: [&str; 3];
    let mut _2: &str;
    let mut _3: &str;
    let mut _4: &str;
    let mut _5: &str;

    bb0: {
        _3 = const "b";
        _2 = &(*_3);
        _5 = const "c";
        _4 = &(*_5);
        _1 = [const "a", move _2, move _4];
        _0 = &_1;
        return;
    }
}
```

…iaskrgr

Rollup of 8 pull requests

Successful merges:

 - rust-lang#121754 ([bootstrap] Move the `split-debuginfo` setting to the per-target section)
 - rust-lang#122205 (ensure that sysroot is properly set for cross-targets)
 - rust-lang#122275 (disable OOM test in Miri)
 - rust-lang#122276 (io::Read trait: make it more clear when we are adressing implementations vs callers)
 - rust-lang#122286 (use Instance::expect_resolve() instead of unwraping Instance::resolve())
 - rust-lang#122290 (MIR printing: print the path of uneval'd const)
 - rust-lang#122293 (diagnostics: Do not suggest using `#[unix_sigpipe]` without a value)
 - rust-lang#122297 (bootstrap: document what the triples in 'Build' mean)

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

…iaskrgr

Rollup of 9 pull requests

Successful merges:

 - rust-lang#122275 (disable OOM test in Miri)
 - rust-lang#122276 (io::Read trait: make it more clear when we are adressing implementations vs callers)
 - rust-lang#122277 (BorrowedCursor docs clarification)
 - rust-lang#122286 (use Instance::expect_resolve() instead of unwraping Instance::resolve())
 - rust-lang#122290 (MIR printing: print the path of uneval'd const)
 - rust-lang#122293 (diagnostics: Do not suggest using `#[unix_sigpipe]` without a value)
 - rust-lang#122297 (bootstrap: document what the triples in 'Build' mean)
 - rust-lang#122302 (docs: Correct ptr/ref verbiage in SliceIndex docs.)
 - rust-lang#122304 (fix metadata for dyn-star in new solver)

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

Rollup merge of rust-lang#122290 - RalfJung:mir-printing, r=compiler-errors

MIR printing: print the path of uneval'd const

Currently it just prints `const _` which makes it impossible to say which constant is being referred to.

Also refer to promoteds in a consistent way; previously MIR printing would do
```
promoted[0] in C1: &Option<Cell<i32>> = {
    // ...
}
```
Now that should be
```
const C1::promoted[0]: &Option<Cell<i32>> = {
    // ...
}
```

We don't seem to have a test for that so I tried it by hand, it seems to work:
```
const main::promoted[12]: &[&str; 3] = {
    let mut _0: &[&str; 3];
    let mut _1: [&str; 3];
    let mut _2: &str;
    let mut _3: &str;
    let mut _4: &str;
    let mut _5: &str;

    bb0: {
        _3 = const "b";
        _2 = &(*_3);
        _5 = const "c";
        _4 = &(*_5);
        _1 = [const "a", move _2, move _4];
        _0 = &_1;
        return;
    }
}
```