allowed to trigger unwinding.

aborting immediately.

The panic handler is called with a special flag which forces it to abort
after calling the panic hook.

I have found this code very confusing at times. This commit clarifies
things.

In particular, the commit explains the requirements that the `Borrow`
impls put on the `Eq` and `Hash` impls, which are non-obvious. And it
puts the `Borrow` impls first, since they force `Eq` and `Hash` to have
particular forms.

The commit also notes `TyS`'s uniqueness requirements.

- Fix style errors.

- L4-bender does not yet support dynamic linking.

- Stack unwinding is not yet supported for x86_64-unknown-l4re-uclibc.
  For now, just abort on panics.

- Use GNU-style linker options where possible. As suggested by review:
    - Use standard GNU-style ld syntax for relro flags.
    - Use standard GNU-style optimization flags and logic.
    - Use standard GNU-style ld syntax for --subsystem.

- Don't read environment variables in L4Bender linker. Thanks to
  CARGO_ENCODED_RUSTFLAGS introduced in rust-lang#9601, l4-bender's arguments can
  now be passed from the L4Re build system without resorting to custom
  parsing of environment variables.

Transition unsupported naked functions future incompatibility lint into
an error:

* Naked functions must contain a single inline assembly block.
  Introduced as future incompatibility lint in 1.50 rust-lang#79653.
  Change into an error fixes a soundness issue described in rust-lang#32489.

* Naked functions must not use any forms of inline attribute.
  Introduced as future incompatibility lint in 1.56 rust-lang#87652.

Generator drop tracking caused an ICE for generators involving the Never
type (Issue rust-lang#93161). Since this breaks miri, we temporarily disable drop
tracking so miri is unblocked while we properly fix the issue.

… doc

…henkov

add support for the l4-bender linker on the x86_64-unknown-l4re-uclibc tier 3 target

This PR contains the work by `@humenda` to update support for the `x86_64-unknown-l4re-uclibc` tier 3 target (published at [humenda/rust](https://github.com/humenda/rust)), rebased and adapted to current rust in follow up commits by myself. The publishing of the rebased changes is authorized and preferred by the original author. As the goal was to distort the original work as little as possible, individual commits introduce changes that are incompatible to the newer code base that the changes were rebased on. These incompatibilities have been remedied in follow up commits, so that the PR as a whole should result in a clean update of the target.
If you prefer another strategy to mainline these changes while preserving attribution, please let me know.

Print a helpful message if unwinding aborts when it reaches a nounwind function

This is implemented by routing `TerminatorKind::Abort` back through the panic handler, but with a special flag in the `PanicInfo` which indicates that the panic handler should *not* attempt to unwind the stack and should instead abort immediately.

This is useful for the planned change in rust-lang/lang-team#97 which would make `Drop` impls `nounwind` by default.

### Code

```rust
#![feature(c_unwind)]

fn panic() {
    panic!()
}

extern "C" fn nounwind() {
    panic();
}

fn main() {
    nounwind();
}
```

### Before

```
$ ./test
thread 'main' panicked at 'explicit panic', test.rs:4:5
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
Illegal instruction (core dumped)
```

### After

```
$ ./test
thread 'main' panicked at 'explicit panic', test.rs:4:5
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
thread 'main' panicked at 'panic in a function that cannot unwind', test.rs:7:1
stack backtrace:
   0:     0x556f8f86ec9b - <std::sys_common::backtrace::_print::DisplayBacktrace as core::fmt::Display>::fmt::hdccefe11a6ac4396
   1:     0x556f8f88ac6c - core::fmt::write::he152b28c41466ebb
   2:     0x556f8f85d6e2 - std::io::Write::write_fmt::h0c261480ab86f3d3
   3:     0x556f8f8654fa - std::panicking::default_hook::{{closure}}::h5d7346f3ff7f6c1b
   4:     0x556f8f86512b - std::panicking::default_hook::hd85803a1376cac7f
   5:     0x556f8f865a91 - std::panicking::rust_panic_with_hook::h4dc1c5a3036257ac
   6:     0x556f8f86f079 - std::panicking::begin_panic_handler::{{closure}}::hdda1d83c7a9d34d2
   7:     0x556f8f86edc4 - std::sys_common::backtrace::__rust_end_short_backtrace::h5b70ed0cce71e95f
   8:     0x556f8f865592 - rust_begin_unwind
   9:     0x556f8f85a764 - core::panicking::panic_no_unwind::h2606ab3d78c87899
  10:     0x556f8f85b910 - test::nounwind::hade6c7ee65050347
  11:     0x556f8f85b936 - test::main::hdc6e02cb36343525
  12:     0x556f8f85b7e3 - core::ops::function::FnOnce::call_once::h4d02663acfc7597f
  13:     0x556f8f85b739 - std::sys_common::backtrace::__rust_begin_short_backtrace::h071d40135adb0101
  14:     0x556f8f85c149 - std::rt::lang_start::{{closure}}::h70dbfbf38b685e93
  15:     0x556f8f85c791 - std::rt::lang_start_internal::h798f1c0268d525aa
  16:     0x556f8f85c131 - std::rt::lang_start::h476a7ee0a0bb663f
  17:     0x556f8f85b963 - main
  18:     0x7f64c0822b25 - __libc_start_main
  19:     0x556f8f85ae8e - _start
  20:                0x0 - <unknown>
thread panicked while panicking. aborting.
Aborted (core dumped)
```

…elid

Update pulldown-cmark version to fix markdown list issue

Fixes rust-lang#92971.

r? `@camelid`

Simplify use of `map_or`

…on, r=oli-obk

Increase the format version of rustdoc-json-types

PR rust-lang#87648 changed `rustdoc-json-types` without increasing the format version.
rust-lang@e7529d6#diff-ede26372490522288745c5b3df2b6b2a1cc913dcd09b29af3a49935afe00c7e6

This PR increase the format version by +1 and move the `FORMAT_VERSION` constant to the start of the file to hopefully make it more clear that `rustdoc-json-types` is versioned.

Interner cleanups

Improve some code that I have found confusing.

r? `@lcnr`

…nctions, r=Amanieu

Reject unsupported naked functions

Transition unsupported naked functions future incompatibility lint into an error:

* Naked functions must contain a single inline assembly block. Introduced as future incompatibility lint in 1.50 rust-lang#79653. Change into an error fixes a soundness issue described in rust-lang#32489.

* Naked functions must not use any forms of inline attribute. Introduced as future incompatibility lint in 1.56 rust-lang#87652.

Closes rust-lang#32490.
Closes rust-lang#32489.

r? `@Amanieu` `@npmccallum` `@joshtriplett`

…ng, r=nikomatsakis

Disable drop range tracking in generators

Generator drop tracking caused an ICE for generators involving the Never type (Issue rust-lang#93161). Since this breaks a test case with miri, we temporarily disable drop tracking so miri is unblocked while we properly fix the issue.

update uclibc instructions for new toolchain, add link from platforms doc

2 quick things:
1) `libc` was updated to make use of features in a uclibc version more recent than the recommended toolchain in the target document, so I updated the link.
2) As has been done with other platforms, link directly from the platform support doc to the target-specific document.

…ns, r=jsha

Add missing GUI test explanations

Some GUI tests didn't have a global explanation about what they were testing. This fixes it.

r? `@jsha`

rustdoc: remove dashed underline under main heading

This was removed in rust-lang#92797 but accidentally re-introduced by a bad merge in rust-lang#92861.

r? `@camelid`