add unstable -Zroot-dir flag to configure the path from which rustc should be invoked

This implements the proposal described [here](#9887 (comment)): we add a new flag, for now called `-Zroot-dir`, that configures the directory relative to which rustc is given the crate root filenames to build. (Files outside this directory are passed absolutely.)

This is necessary to be able to fix (no github don't close that issue yet) rust-lang/rust#128726: in multi-workspace repositories that use scripts to manage a whole bunch of cargo invocations, currently the output cargo+rustc produce is often hard or even impossible to interpret for both human and machine consumption. This is because directories in the output are always relative to the workspace root, but when cargo is invoked many times for different workspaces, it is quite unclear what the workspace root is for the invocation that failed.

So I suggest we should have a new flag that the build script in such a repo can set to the consistent "root dir" that the user would recognize as such (e.g., the root of the rustc source tree), and all paths emitted by cargo and rustc should be relative to that directory.

I don't know all the places that cargo itself emits paths (if any), but this PR changes the way we invoke rustc to honor the new flag, so all paths emitted by rustc will be relative to the `-Zroot-dir`.

See rust-lang/rust#132390 for the changes needed in rustc bootstrap to wire this up; together, that suffices to finally properly show errors in RA for all parts of the rustc src tree. :)

Pkgsrc changes relative to rust184:

 * patch reorganization to deal with new version
   of upstream vendored crates, checksum updates.

Version 1.85.0 (2025-02-20)
==========================

Language
--------
- [The 2024 Edition is now stable.]
  (rust-lang/rust#133349)
  See [the edition guide]
  (https://doc.rust-lang.org/nightly/edition-guide/rust-2024/index.html)
  for more details.
- [Stabilize async closures]
  (rust-lang/rust#132706)
  See [RFC 3668]
  (https://rust-lang.github.io/rfcs/3668-async-closures.html) for more details.
- [Stabilize `#[diagnostic::do_not_recommend]`]
  (rust-lang/rust#132056)
- [Add `unpredictable_function_pointer_comparisons` lint to warn
  against function pointer comparisons]
  (rust-lang/rust#118833)
- [Lint on combining `#[no_mangle]` and `#[export_name]` attributes.]
  (rust-lang/rust#131558)

Compiler
--------
- [The unstable flag `-Zpolymorphize` has been removed]
  (rust-lang/rust#133883), see
  rust-lang/compiler-team#810 for some
  background.

Platform Support
----------------
- [Promote `powerpc64le-unknown-linux-musl` to tier 2 with host tools]
  (rust-lang/rust#133801)

Refer to Rust's [platform support page][platform-support-doc]
for more information on Rust's tiered platform support.

Libraries
---------
- [Panics in the standard library now have a leading `library/` in their path]
  (rust-lang/rust#132390)
- [`std::env::home_dir()` on Windows now ignores the non-standard
  `$HOME` environment variable]
  (rust-lang/rust#132515)

  It will be un-deprecated in a subsequent release.
- [Add `AsyncFn*` to the prelude in all editions.]
  (rust-lang/rust#132611)

Stabilized APIs
---------------

- [`BuildHasherDefault::new`]
  (https://doc.rust-lang.org/stable/std/hash/struct.BuildHasherDefault.html#method.new)
- [`ptr::fn_addr_eq`]
  (https://doc.rust-lang.org/std/ptr/fn.fn_addr_eq.html)
- [`io::ErrorKind::QuotaExceeded`]
  (https://doc.rust-lang.org/stable/std/io/enum.ErrorKind.html#variant.QuotaExceeded)
- [`io::ErrorKind::CrossesDevices`]
  (https://doc.rust-lang.org/stable/std/io/enum.ErrorKind.html#variant.CrossesDevices)
- [`{float}::midpoint`]
  (https://doc.rust-lang.org/core/primitive.f32.html#method.midpoint)
- [Unsigned `{integer}::midpoint`]
  (https://doc.rust-lang.org/std/primitive.u64.html#method.midpoint)
- [`NonZeroU*::midpoint`]
  (https://doc.rust-lang.org/std/num/type.NonZeroU32.html#method.midpoint)
- [impl `std::iter::Extend` for tuples with arity 1 through 12]
  (https://doc.rust-lang.org/stable/std/iter/trait.Extend.html#impl-Extend%3C(A,)%3E-for-(EA,))
- [`FromIterator<(A, ...)>` for tuples with arity 1 through 12]
  (https://doc.rust-lang.org/stable/std/iter/trait.FromIterator.html#impl-FromIterator%3C(EA,)%3E-for-(A,))
- [`std::task::Waker::noop`]
  (https://doc.rust-lang.org/stable/std/task/struct.Waker.html#method.noop)

These APIs are now stable in const contexts:

- [`mem::size_of_val`]
  (https://doc.rust-lang.org/stable/std/mem/fn.size_of_val.html)
- [`mem::align_of_val`]
  (https://doc.rust-lang.org/stable/std/mem/fn.align_of_val.html)
- [`Layout::for_value`]
  (https://doc.rust-lang.org/stable/std/alloc/struct.Layout.html#method.for_value)
- [`Layout::align_to`]
  (https://doc.rust-lang.org/stable/std/alloc/struct.Layout.html#method.align_to)
- [`Layout::pad_to_align`]
  (https://doc.rust-lang.org/stable/std/alloc/struct.Layout.html#method.pad_to_align)
- [`Layout::extend`]
  (https://doc.rust-lang.org/stable/std/alloc/struct.Layout.html#method.extend)
- [`Layout::array`]
  (https://doc.rust-lang.org/stable/std/alloc/struct.Layout.html#method.array)
- [`std::mem::swap`]
  (https://doc.rust-lang.org/stable/std/mem/fn.swap.html)
- [`std::ptr::swap`]
  (https://doc.rust-lang.org/stable/std/ptr/fn.swap.html)
- [`NonNull::new`]
  (https://doc.rust-lang.org/stable/std/ptr/struct.NonNull.html#method.new)
- [`HashMap::with_hasher`]
  (https://doc.rust-lang.org/stable/std/collections/struct.HashMap.html#method.with_hasher)
- [`HashSet::with_hasher`]
  (https://doc.rust-lang.org/stable/std/collections/struct.HashSet.html#method.with_hasher)
- [`BuildHasherDefault::new`]
  (https://doc.rust-lang.org/stable/std/hash/struct.BuildHasherDefault.html#method.new)
- [`<float>::recip`]
  (https://doc.rust-lang.org/stable/std/primitive.f32.html#method.recip)
- [`<float>::to_degrees`]
  (https://doc.rust-lang.org/stable/std/primitive.f32.html#method.to_degrees)
- [`<float>::to_radians`]
  (https://doc.rust-lang.org/stable/std/primitive.f32.html#method.to_radians)
- [`<float>::max`]
  (https://doc.rust-lang.org/stable/std/primitive.f32.html#method.max)
- [`<float>::min`]
  (https://doc.rust-lang.org/stable/std/primitive.f32.html#method.min)
- [`<float>::clamp`]
  (https://doc.rust-lang.org/stable/std/primitive.f32.html#method.clamp)
- [`<float>::abs`]
  (https://doc.rust-lang.org/stable/std/primitive.f32.html#method.abs)
- [`<float>::signum`]
  (https://doc.rust-lang.org/stable/std/primitive.f32.html#method.signum)
- [`<float>::copysign`]
  (https://doc.rust-lang.org/stable/std/primitive.f32.html#method.copysign)
- [`MaybeUninit::write`]
  (https://doc.rust-lang.org/stable/std/mem/union.MaybeUninit.html#method.write)

Cargo
-----
- [Add future-incompatibility warning against keywords in cfgs and
  add raw-idents] (rust-lang/cargo#14671)
- [Stabilize higher precedence trailing flags]
  (rust-lang/cargo#14900)
- [Pass `CARGO_CFG_FEATURE` to build scripts]
  (rust-lang/cargo#14902)

Rustdoc
-----
- [Doc comment on impl blocks shows the first line, even when the
  impl block is collapsed] (rust-lang/rust#132155)

Compatibility Notes
-------------------
- [`rustc` no longer treats the `test` cfg as a well known
  check-cfg] (rust-lang/rust#131729),
  instead it is up to the build systems and users of
  `--check-cfg`[^check-cfg] to set it as a well known cfg using
  `--check-cfg=cfg(test)`.

  This is done to enable build systems like Cargo to set it
  conditionally, as not all source files are suitable for unit
  tests.

  [Cargo (for now) unconditionally sets the `test` cfg as a well known cfg]
  (rust-lang/cargo#14963).
  [^check-cfg]: https://doc.rust-lang.org/nightly/rustc/check-cfg.html

- [Disable potentially incorrect type inference if there are trivial
  and non-trivial where-clauses]
  (rust-lang/rust#132325)

- `std::env::home_dir()` has been deprecated for years, because it
  can give surprising results in some Windows configurations if the
  `HOME` environment variable is set (which is not the normal
  configuration on Windows). We had previously avoided changing its
  behavior, out of concern for compatibility with code depending on
  this non-standard configuration. Given how long this function has
  been deprecated, we're now fixing its behavior as a bugfix. A
  subsequent release will remove the deprecation for this function.

- [Make `core::ffi::c_char` signedness more closely match that of
  the platform-default `char`]
  (rust-lang/rust#132975)

  This changed `c_char` from an `i8` to `u8` or vice versa on many
  Tier 2 and 3 targets (mostly Arm and RISC-V embedded targets).
  The new definition may result in compilation failures but fixes
  compatibility issues with C.

  The `libc` crate matches this change as of its 0.2.169 release.

- [When compiling a nested `macro_rules` macro from an external
  crate, the content of the inner `macro_rules` is now built with
  the edition of the external crate, not the local crate.]
  (rust-lang/rust#133274)
- [Increase `sparcv9-sun-solaris` and `x86_64-pc-solaris` Solaris
  baseline to 11.4.]
  (rust-lang/rust#133293)
- [Show `abi_unsupported_vector_types` lint in future breakage reports]
  (rust-lang/rust#133374)
- [Error if multiple super-trait instantiations of `dyn Trait` need
  associated types to be specified but only one is provided]
  (rust-lang/rust#133392)
- [Change `powerpc64-ibm-aix` default `codemodel` to large]
  (rust-lang/rust#133811)

Internal Changes
----------------

These changes do not affect any public interfaces of Rust, but they
represent significant improvements to the performance or internals
of rustc and related tools.

- [Build `x86_64-unknown-linux-gnu` with LTO for C/C++ code (e.g., `jemalloc`)]
  (rust-lang/rust#134690)

This MR contains the following updates:

| Package | Update | Change |
|---|---|---|
| [rust](https://github.com/rust-lang/rust) | minor | `1.84.1` -> `1.85.0` |

MR created with the help of [el-capitano/tools/renovate-bot](https://gitlab.com/el-capitano/tools/renovate-bot).

**Proposed changes to behavior should be submitted there as MRs.**

---

### Release Notes

<details>
<summary>rust-lang/rust (rust)</summary>

### [`v1.85.0`](https://github.com/rust-lang/rust/blob/HEAD/RELEASES.md#Version-1850-2025-02-20)

[Compare Source](rust-lang/rust@1.84.1...1.85.0)

\==========================

<a id="1.85.0-Language"></a>

## Language

-   [The 2024 Edition is now stable.](rust-lang/rust#133349)
    See [the edition guide](https://doc.rust-lang.org/nightly/edition-guide/rust-2024/index.html) for more details.
-   [Stabilize async closures](rust-lang/rust#132706)
    See [RFC 3668](https://rust-lang.github.io/rfcs/3668-async-closures.html) for more details.
-   [Stabilize `#[diagnostic::do_not_recommend]`](rust-lang/rust#132056)
-   [Add `unpredictable_function_pointer_comparisons` lint to warn against function pointer comparisons](rust-lang/rust#118833)
-   [Lint on combining `#[no_mangle]` and `#[export_name]` attributes.](rust-lang/rust#131558)

<a id="1.85.0-Compiler"></a>

## Compiler

-   [The unstable flag `-Zpolymorphize` has been removed](rust-lang/rust#133883), see rust-lang/compiler-team#810 for some background.

<a id="1.85.0-Platform-Support"></a>

## Platform Support

-   [Promote `powerpc64le-unknown-linux-musl` to tier 2 with host tools](rust-lang/rust#133801)

Refer to Rust's \[platform support page]\[platform-support-doc]
for more information on Rust's tiered platform support.

<a id="1.85.0-Libraries"></a>

## Libraries

-   [Panics in the standard library now have a leading `library/` in their path](rust-lang/rust#132390)
-   [`std::env::home_dir()` on Windows now ignores the non-standard `$HOME` environment variable](rust-lang/rust#132515)

    It will be un-deprecated in a subsequent release.
-   [Add `AsyncFn*` to the prelude in all editions.](rust-lang/rust#132611)

<a id="1.85.0-Stabilized-APIs"></a>

## Stabilized APIs

-   [`BuildHasherDefault::new`](https://doc.rust-lang.org/stable/std/hash/struct.BuildHasherDefault.html#method.new)
-   [`ptr::fn_addr_eq`](https://doc.rust-lang.org/std/ptr/fn.fn_addr_eq.html)
-   [`io::ErrorKind::QuotaExceeded`](https://doc.rust-lang.org/stable/std/io/enum.ErrorKind.html#variant.QuotaExceeded)
-   [`io::ErrorKind::CrossesDevices`](https://doc.rust-lang.org/stable/std/io/enum.ErrorKind.html#variant.CrossesDevices)
-   [`{float}::midpoint`](https://doc.rust-lang.org/core/primitive.f32.html#method.midpoint)
-   [Unsigned `{integer}::midpoint`](https://doc.rust-lang.org/std/primitive.u64.html#method.midpoint)
-   [`NonZeroU*::midpoint`](https://doc.rust-lang.org/std/num/type.NonZeroU32.html#method.midpoint)
-   [impl `std::iter::Extend` for tuples with arity 1 through 12](https://doc.rust-lang.org/stable/std/iter/trait.Extend.html#impl-Extend%3C\(A,\)%3E-for-\(EA,\))
-   [`FromIterator<(A, ...)>` for tuples with arity 1 through 12](https://doc.rust-lang.org/stable/std/iter/trait.FromIterator.html#impl-FromIterator%3C\(EA,\)%3E-for-\(A,\))
-   [`std::task::Waker::noop`](https://doc.rust-lang.org/stable/std/task/struct.Waker.html#method.noop)

These APIs are now stable in const contexts:

-   [`mem::size_of_val`](https://doc.rust-lang.org/stable/std/mem/fn.size_of_val.html)
-   [`mem::align_of_val`](https://doc.rust-lang.org/stable/std/mem/fn.align_of_val.html)
-   [`Layout::for_value`](https://doc.rust-lang.org/stable/std/alloc/struct.Layout.html#method.for_value)
-   [`Layout::align_to`](https://doc.rust-lang.org/stable/std/alloc/struct.Layout.html#method.align_to)
-   [`Layout::pad_to_align`](https://doc.rust-lang.org/stable/std/alloc/struct.Layout.html#method.pad_to_align)
-   [`Layout::extend`](https://doc.rust-lang.org/stable/std/alloc/struct.Layout.html#method.extend)
-   [`Layout::array`](https://doc.rust-lang.org/stable/std/alloc/struct.Layout.html#method.array)
-   [`std::mem::swap`](https://doc.rust-lang.org/stable/std/mem/fn.swap.html)
-   [`std::ptr::swap`](https://doc.rust-lang.org/stable/std/ptr/fn.swap.html)
-   [`NonNull::new`](https://doc.rust-lang.org/stable/std/ptr/struct.NonNull.html#method.new)
-   [`HashMap::with_hasher`](https://doc.rust-lang.org/stable/std/collections/struct.HashMap.html#method.with_hasher)
-   [`HashSet::with_hasher`](https://doc.rust-lang.org/stable/std/collections/struct.HashSet.html#method.with_hasher)
-   [`BuildHasherDefault::new`](https://doc.rust-lang.org/stable/std/hash/struct.BuildHasherDefault.html#method.new)
-   [`<float>::recip`](https://doc.rust-lang.org/stable/std/primitive.f32.html#method.recip)
-   [`<float>::to_degrees`](https://doc.rust-lang.org/stable/std/primitive.f32.html#method.to_degrees)
-   [`<float>::to_radians`](https://doc.rust-lang.org/stable/std/primitive.f32.html#method.to_radians)
-   [`<float>::max`](https://doc.rust-lang.org/stable/std/primitive.f32.html#method.max)
-   [`<float>::min`](https://doc.rust-lang.org/stable/std/primitive.f32.html#method.min)
-   [`<float>::clamp`](https://doc.rust-lang.org/stable/std/primitive.f32.html#method.clamp)
-   [`<float>::abs`](https://doc.rust-lang.org/stable/std/primitive.f32.html#method.abs)
-   [`<float>::signum`](https://doc.rust-lang.org/stable/std/primitive.f32.html#method.signum)
-   [`<float>::copysign`](https://doc.rust-lang.org/stable/std/primitive.f32.html#method.copysign)
-   [`MaybeUninit::write`](https://doc.rust-lang.org/stable/std/mem/union.MaybeUninit.html#method.write)

<a id="1.85.0-Cargo"></a>

## Cargo

-   [Add future-incompatibility warning against keywords in cfgs and add raw-idents](rust-lang/cargo#14671)
-   [Stabilize higher precedence trailing flags](rust-lang/cargo#14900)
-   [Pass `CARGO_CFG_FEATURE` to build scripts](rust-lang/cargo#14902)

<a id="1.85.0-Rustdoc"></a>

## Rustdoc

-   [Doc comment on impl blocks shows the first line, even when the impl block is collapsed](rust-lang/rust#132155)

<a id="1.85.0-Compatibility-Notes"></a>

## Compatibility Notes

-   [`rustc` no longer treats the `test` cfg as a well known check-cfg](rust-lang/rust#131729), instead it is up to the build systems and users of `--check-cfg`\[^check-cfg] to set it as a well known cfg using `--check-cfg=cfg(test)`.

    This is done to enable build systems like Cargo to set it conditionally, as not all source files are suitable for unit tests.
    [Cargo (for now) unconditionally sets the `test` cfg as a well known cfg](rust-lang/cargo#14963).
    \[^check-cfg]: https://doc.rust-lang.org/nightly/rustc/check-cfg.html
-   [Disable potentially incorrect type inference if there are trivial and non-trivial where-clauses](rust-lang/rust#132325)
-   `std::env::home_dir()` has been deprecated for years, because it can give surprising results in some Windows configurations if the `HOME` environment variable is set (which is not the normal configuration on Windows). We had previously avoided changing its behavior, out of concern for compatibility with code depending on this non-standard configuration. Given how long this function has been deprecated, we're now fixing its behavior as a bugfix. A subsequent release will remove the deprecation for this function.
-   [Make `core::ffi::c_char` signedness more closely match that of the platform-default `char`](rust-lang/rust#132975)

    This changed `c_char` from an `i8` to `u8` or vice versa on many Tier 2 and 3
    targets (mostly Arm and RISC-V embedded targets). The new definition may
    result in compilation failures but fixes compatibility issues with C.

    The `libc` crate matches this change as of its 0.2.169 release.
-   [When compiling a nested `macro_rules` macro from an external crate, the content of the inner `macro_rules` is now built with the edition of the external crate, not the local crate.](rust-lang/rust#133274)
-   [Increase `sparcv9-sun-solaris` and `x86_64-pc-solaris` Solaris baseline to 11.4.](rust-lang/rust#133293)
-   [Show `abi_unsupported_vector_types` lint in future breakage reports](rust-lang/rust#133374)
-   [Error if multiple super-trait instantiations of `dyn Trait` need associated types to be specified but only one is provided](rust-lang/rust#133392)
-   [Change `powerpc64-ibm-aix` default `codemodel` to large](rust-lang/rust#133811)

<a id="1.85.0-Internal-Changes"></a>

## Internal Changes

These changes do not affect any public interfaces of Rust, but they represent
significant improvements to the performance or internals of rustc and related
tools.

-   [Build `x86_64-unknown-linux-gnu` with LTO for C/C++ code (e.g., `jemalloc`)](rust-lang/rust#134690)

</details>

---

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🔕 **Ignore**: Close this MR and you won't be reminded about this update again.

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