The body_span was assumed to be in the Span root context, but this was
not the case for async function bodies.

And make the LocalDecl internal, to avoid needing to declare storage.
(For multiple `continue` stateuemtns, it must also be mutable.)

`continue` statements were missing coverage. This was particularly
noticeable in a match pattern that contained only a `continue`
statement, leaving the branch appear uncounted. This PR addresses the
problem and adds tests to prove it.

`fast-math` implies things like functions not being able to accept as an
argument or return as a result, say, `inf` which made these functions
confusingly named or behaving incorrectly, depending on how you
interpret it. Since the time when these intrinsics have been implemented
the intrinsics user's (stdsimd) approach has changed significantly and
so now it is required that these intrinsics operate normally rather than
in "whatever" way.

Fixes #84268

Fixes #84252

This query reads from untracked global state in `CStore`.

This option influences monomorphization, which participates in
incremental compilation.

Fixes #84195

LLVM supports many functions from math.h in its IR. Many of these have
single-instruction variants on various platforms. So, let's add them so
std::arch can use them.

Yes, exact comparison is intentional: rounding must always return a
valid integer-equal value, except for inf/NAN.

An error is already created by AST validation.

By simply swapping the calls to `map` and `and_then` around the complexity of
handling an `Option<Option<_>>` disappears.

 ### Background

    In #76570, new ABI strings including `C-unwind` were introduced.
    Their behavior is specified in RFC 2945 [1].

    However, it was reported in the #ffi-unwind stream of the Rust
    community Zulip that this had altered the way that `extern "C"`
    functions behaved even when the `c_unwind` feature gate was not
    active. [2]

 ### Overview

    This makes a small patch to
    `rustc_mir_build::build::should_abort_on_panic`, so that the same
    behavior from before is in place when the `c_unwind` gate is not
    active.

    `rustc_middle::ty::layout::fn_can_unwind` is not touched, as the
    visible behavior should not differ before/after #76570. [3]

 ### Footnotes

 [1]: https://github.com/rust-lang/rfcs/blob/master/text/2945-c-unwind-abi.md
 [2]: https://rust-lang.zulipchat.com/#narrow/stream/210922-project-ffi-unwind/topic/Is.20unwinding.20through.20extern.20C.20UB.3F/near/230112325
 [3]: https://github.com/rust-lang/rust/pull/76570/files#diff-b0320c2b8868f325d83c027fc5d71732636e9763551e35895488f30fe057c6e9L2599-R2617

This message is emitted as guidance by the compiler when a developer attempts to reassign a value to an immutable variable.  Following the message will always currently work, but it may not always be the best course of action; following the 'consider ...' messaging pattern provides a hint to the developer that it could be wise to explore other alternatives.

Also tweaked the message a bit by

- removing the hyphen, because in my opinion the hyphen makes the
  message a bit harder to read, especially combined with the backticks;
- adding the word "be", because I think it's a bit clearer that way.

This PR modifies the macro expansion infrastructure to handle attributes
in a fully token-based manner. As a result:

* Derives macros no longer lose spans when their input is modified
  by eager cfg-expansion. This is accomplished by performing eager
  cfg-expansion on the token stream that we pass to the derive
  proc-macro
* Inner attributes now preserve spans in all cases, including when we
  have multiple inner attributes in a row.

This is accomplished through the following changes:

* New structs `AttrAnnotatedTokenStream` and `AttrAnnotatedTokenTree` are introduced.
  These are very similar to a normal `TokenTree`, but they also track
  the position of attributes and attribute targets within the stream.
  They are built when we collect tokens during parsing.
  An `AttrAnnotatedTokenStream` is converted to a regular `TokenStream` when
  we invoke a macro.
* Token capturing and `LazyTokenStream` are modified to work with
  `AttrAnnotatedTokenStream`. A new `ReplaceRange` type is introduced, which
  is created during the parsing of a nested AST node to make the 'outer'
  AST node aware of the attributes and attribute target stored deeper in the token stream.
* When we need to perform eager cfg-expansion (either due to `#[derive]` or `#[cfg_eval]`),
we tokenize and reparse our target, capturing additional information about the locations of
`#[cfg]` and `#[cfg_attr]` attributes at any depth within the target.
This is a performance optimization, allowing us to perform less work
in the typical case where captured tokens never have eager cfg-expansion run.

Extract attribute name once and match it against symbols that are being
validated, instead of using `Session::check_name` for each symbol
individually.

Assume that all validated attributes are used, instead of marking them
as such, since the attribute check should be exhaustive.

While derives were being collected in left-to-order order, the
corresponding `Invocation`s were being pushed in the wrong order.

Hint upgrading to a newer Rust version instead