rust: kbuild: disambiguate `zerocopy` for `rusttest`

Starting with Rust 1.76.0, `zerocopy` was added as an (indirect)
compiler dependency [1]. In turn, this meant that the `rustc-dev`
component started including a precompiled `zerocopy` crate in the sysroot.

This makes `rusttest` fail because the compiler finds several candidates:

    error[E0464]: multiple candidates for `rmeta` dependency `zerocopy` found
      --> rust/kernel/prelude.rs:64:9
       |
    64 | pub use zerocopy::{
       |         ^^^^^^^^
       |
       = note: candidate #1: .../lib/rustlib/x86_64-unknown-linux-gnu/lib/libzerocopy-dfef4cb07ca752aa.rmeta
       = note: candidate #2: ./rust/test/libzerocopy.rlib

We cannot use `--sysroot=/dev/null` for these, thus point to the dependency
explicitly.

Assisted-by: Claude:claude-opus-4-8
Signed-off-by: Antoni Boucher <bouanto@zoho.com>
Cc: stable@vger.kernel.org
Fixes: 567621523ab7 ("rust: zerocopy: enable support in kbuild")
Link: https://github.com/rust-lang/rust/pull/118546 [1]
Link: https://patch.msgid.link/20260729173803.13459-1-ojeda@kernel.org
[ Investigated when it started happening, reworded to add that and to
  follow our usual style and sent on behalf of Antoni, who found this
  during his work to support Rust for Linux with the GCC backend, i.e.
  with `rustc_codegen_gcc`. - Miguel ]
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

0 files changed, 0 insertions, 0 deletions