This commit moves the compiler-builtins-specific build logic from
`src/bootstrap/bin/rustc.rs` into the workspace `Cargo.toml`'s
`[profile]` configuration. Now that rust-lang/cargo#7253 is fixed we can
ensure that Cargo knows about debug assertions settings, and it can also
be configured to specifically disable debug assertions unconditionally
for compiler-builtins. This should improve rebuild logic when
debug-assertions settings change and also improve build-std integration
where Cargo externally now has an avenue to learn how to build
compiler-builtins as well.

Make it possible to customize the location of musl libdir using
musl-libdir in config.toml, e.g., to use lib64 instead of lib.

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

…g-assertions, r=Mark-Simulacrum

rustbuild: Move compiler-builtins build logic to manifest

This commit moves the compiler-builtins-specific build logic from
`src/bootstrap/bin/rustc.rs` into the workspace `Cargo.toml`'s
`[profile]` configuration. Now that rust-lang/cargo#7253 is fixed we can
ensure that Cargo knows about debug assertions settings, and it can also
be configured to specifically disable debug assertions unconditionally
for compiler-builtins. This should improve rebuild logic when
debug-assertions settings change and also improve build-std integration
where Cargo externally now has an avenue to learn how to build
compiler-builtins as well.

bootstrap: Configurable musl libdir

Make it possible to customize the location of musl libdir using
musl-libdir in config.toml, e.g., to use lib64 instead of lib.

…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

…hievink

Remove blank line