Fix rust-lang#59326.

Speedup vec![1_i8; N] for non-zero element.

Before
test do_bench_from_elem_i8        ... bench:         130 ns/iter (+/- 7) = 61 MB/s
test do_bench_from_elem_u8        ... bench:         121 ns/iter (+/- 4) = 66 MB/s
After
test do_bench_from_elem_i8        ... bench:         123 ns/iter (+/- 7) = 65 MB/s
test do_bench_from_elem_u8        ... bench:         121 ns/iter (+/- 5) = 66 MB/s

No speed difference if element is already zero.

    #[bench]
    fn do_bench_from_elem_i8(b: &mut Bencher) {
        b.bytes = 8 as u64;
        b.iter(|| {
            let dst = ve::vec![10_i8; 100];
            assert_eq!(dst.len(), 100);
            assert!(dst.iter().all(|x| *x == 10));
        })
    }

As suggested by @cuviper
https://rust-lang.zulipchat.com/#narrow/stream/219381-t-libs/topic/SpecForElem.20for.20other.20integers

Co-authored-by: Bastian Kauschke <bastian_kauschke@hotmail.de>

- Pass around document_private a lot more
- Add tests
  + Add tests for intra-doc links to private items
  + Add ignored tests for warnings in reference links

Warn if linking to a private item

Closes rust-lang#72769

r? @GuillaumeGomez

Fortanix SGX target libunwind build process changes

Ticket: fortanix/rust-sgx#174
LLVM related changes (merged): rust-lang/llvm-project#57

Description: libunwind changes needed to run code in sgx environment via rust-sgx.

Target that uses this in rust: x86_64-fortanix-unknown-sgx.

Without this change, rust std for this toolchain is forced to use a precompiled library loaded via environment variable.

With this change we act the same as musl target.

Perform obligation deduplication to avoid buggy `ExistentialMismatch`

Address rust-lang#59326.

…r=cuviper

Add liballoc impl SpecFromElem for i8

Speedup vec![1_i8; N] for non-zero element.

Before
test do_bench_from_elem_i8        ... bench:         130 ns/iter (+/- 7) = 61 MB/s
test do_bench_from_elem_u8        ... bench:         121 ns/iter (+/- 4) = 66 MB/s
After
test do_bench_from_elem_i8        ... bench:         123 ns/iter (+/- 7) = 65 MB/s
test do_bench_from_elem_u8        ... bench:         121 ns/iter (+/- 5) = 66 MB/s

No speed difference if element is already zero.

```rust
#[bench]
fn do_bench_from_elem_i8(b: &mut Bencher) {
    b.bytes = 8 as u64;
    b.iter(|| {
        let dst = ve::vec![10_i8; 100];
        assert_eq!(dst.len(), 100);
        assert!(dst.iter().all(|x| *x == 10));
    })
}
```

As suggested by @cuviper
https://rust-lang.zulipchat.com/#narrow/stream/219381-t-libs/topic/SpecForElem.20for.20other.20integers

r? @cuviper
CC @joshtriplett

Edit: Wow, I just realized both reviewers are Josh.

…aster

add missing doc links

The doc comments contain ``[`size_of_val`]`` but the link target was missing.

…Simulacrum

Shortcuts for min/max on double-ended BTreeMap/BTreeSet iterators

Closes rust-lang#59947: a performance tweak that might benefit some. Optimizes `min` and `max ` on all btree double-ended iterators that do not drop, i.e. the iterators created by:

- `BTreeMap::iter`
- `BTreeMap::iter_mut`
- `BTreeMap::keys` and `BTreeSet::iter`
- `BTreeMap::range` and `BTreeSet::range`
- `BTreeMap::range_mut`

Also in these (currently) single-ended iterators, but obviously for `min` only:
- `BTreeSet::difference`
- `BTreeSet::intersection`
- `BTreeSet::symmetric_difference`
- `BTreeSet::union`

Did not do this in iterators created by `into_iter` to preserve drop order, as outlined in rust-lang#62316.

Did not do this in iterators created by `drain_filter`, possibly to preserve drop order, possibly to preserve predicate invocation, mostly to not have to think about it too hard (I guess maybe it wouldn't be a change for `min`, which is the only shortcut possible in this single-ended iterator).

…=Mark-Simulacrum

Bootstrap: detect Windows based on sys.platform

Closes rust-lang#73689.

…Mark-Simulacrum

Document the Self keyword

Partial fix of rust-lang#34601.

Document the `Self` keyword.

This contains simple examples of the places where `Self` can be used.

…aster

Document the super keyword

Partial fix of rust-lang#34601.

Quite short, just a small example and a link to the reference.

@rustbot modify labels: T-doc,C-enhancement

…ywiser

Document some invariants correctly/more

r? @wesleywiser

Remove irrelevant comment

Iterator is no longer a lang item since 216e72f.

…hievink

Remove blank line