PR rust-lang#93918 made it so that `-static-libstdc++` was only set in one place,
and was only set during linking, but accidentally also made it so that
it is no longer passed when building LLD or sanitizers, only when
building LLVM itself. This moves the logic for setting
`-static-libstdc++` in the linker flags back to `configure_cmake` so
that it takes effect for all CMake invocations in `native.rs`.

As a side-effect, this also causes libstdc++ to be statically compiled
into sanitizers and LLD if `llvm-tools-enabled` is set but
`llvm-static-stdcpp` is not, even though previously it was only linked
statically if `llvm-static-stdcpp` was set explicitly. But that seems
more like the expected behavior anyway.

…r=Mark-Simulacrum

Use in-tree libunwind by default on Fuchsia

Fuchsia doesn't ship libunwind in its SDK, so we must provide it statically.

Better error for normalization errors from parent crates that use `#![feature(generic_const_exprs)]`

This PR implements a somewhat rudimentary heuristic to suggest using `#![feature(generic_const_exprs)]` in a child crate when a function from a foreign crate (that may have used `#![feature(generic_const_exprs)]`) fails to normalize during codegen.

cc: rust-lang#79018
cc: rust-lang#94287

…ottmcm

Document new recommended use of `FromIterator::from_iter`

rust-lang#90107
Most of the added prose was paraphrased from the links provided in the issue. The suggested `VecDeque` example seemed to make the point well enough so I just used that.

…ss, r=joshtriplett

Fix soundness issue in scoped threads.

This was discovered in rust-lang#94559 (comment)

The `scope()` function returns when all threads are finished, but I accidentally considered a thread 'finished' before dropping their panic payload or ignored return value.

So if a thread returned (or panics with) something that in its `Drop` implementation still uses borrowed stuff, it goes wrong.

https://play.rust-lang.org/?version=nightly&mode=debug&edition=2021&gist=2a1f19ac4676cdabe43e24e536ff9358

…mulacrum

Statically compile libstdc++ everywhere if asked

PR rust-lang#93918 made it so that `-static-libstdc++` was only set in one place,
and was only set during linking, but accidentally also made it so that
it is no longer passed when building LLD, only when building LLVM
itself. This moves the logic for setting `-static-libstdc++` in the
linker flags to `configure_cmake` so that it takes effect for all CMake
invocations in `native.rs`.

As a side-effect, this also causes libstdc++ to be statically compiled
into sanitizers, whereas previously the `llvm-static-stdcpp` flag had no
effect on sanitizers. It also makes it so that LLD will be compiled
statically if `llvm-tools-enabled` is set, even though previously it was
only linked statically if `llvm-static-stdcpp` was set explicitly. Both
of these seem like they match expected behavior than what was there
prior to rust-lang#93918.

…=notriddle

Unify impl blocks by wrapping them into a div

The blanket and "auto traits" sections are wrapped into a `div` with an ID. This PR fixes this incoherence by wrapping each impl section (the "deref impl" and the "inherent impl" sections were missing it). It'll also make some tests simpler to write.

r? ````@notriddle````

…GuillaumeGomez

Improve rustdoc book

This pull-request improves the `rustdoc` book by doing some (light) cleanup, by merging some stuff, by adding some missing stuff (like tracking issues links, for those who had one) and also by moving some chapter's into sub-chapter's to improve the flow of the book.

~~Note that I locally tested with `mdbook-lintcheck` that no links became accidentally broken.~~ (Not enough, ;-))

r? ````@GuillaumeGomez````