Pull Rust updates from Miguel Ojeda:
 "Another routine one in terms of features. In terms of lines, this time
  the 'alloc' version upgrade is less prominent, given that it was
  fairly small (and we did not have two upgrades)

  Toolchain and infrastructure:

   - Upgrade to Rust 1.74.1

     The patch release includes a fix for an ICE that the Apple AGX GPU
     driver was hitting

   - Support 'srctree'-relative links in Rust code documentation

   - Automate part of the manual constants handling (i.e. the ones not
     recognised by 'bindgen')

   - Suppress searching builtin sysroot to avoid confusion with
     installed sysroots, needed for the to-be-merged arm64 support which
     uses a builtin target

   - Ignore '__preserve_most' functions for 'bindgen'

   - Reduce header inclusion bloat in exports

  'kernel' crate:

   - Implement 'Debug' for 'CString'

   - Make 'CondVar::wait()' an uninterruptible wait

  'macros' crate:

   - Update 'paste!' to accept string literals

   - Improve '#[vtable]' documentation

  Documentation:

   - Add testing section (KUnit and 'rusttest' target)

   - Remove 'CC=clang' mentions

   - Clarify that 'rustup override' applies to build directory"

* tag 'rust-6.8' of https://github.com/Rust-for-Linux/linux:
  docs: rust: Clarify that 'rustup override' applies to build directory
  docs: rust: Add rusttest info
  docs: rust: remove `CC=clang` mentions
  rust: support `srctree`-relative links
  rust: sync: Makes `CondVar::wait()` an uninterruptible wait
  rust: upgrade to Rust 1.74.1
  rust: Suppress searching builtin sysroot
  rust: macros: improve `#[vtable]` documentation
  rust: macros: update 'paste!' macro to accept string literals
  rust: bindings: rename const binding using sed
  rust: Ignore preserve-most functions
  rust: replace <linux/module.h> with <linux/export.h> in rust/exports.c
  rust: kernel: str: Implement Debug for CString