[PATCH] rust: kbuild: disambiguate `zerocopy_derive` for `rusttest`

The `rustc-dev` components for Rust 1.82.0 through 1.87.0 include a
precompiled `zerocopy_derive` procedural macro in the sysroot. This
range includes Rust 1.85.0, our minimum supported version.

This makes `rusttest` fail because the compiler finds both the sysroot
copy and the copy built in `rust/test`:

    error[E0464]: multiple candidates for `dylib` dependency `zerocopy_derive` found
      --> rust/kernel/prelude.rs:70:9
       |
    70 | pub use zerocopy_derive::{
       |         ^^^^^^^^^^^^^^^
       |
       = note: candidate #1: .../lib/rustlib/x86_64-unknown-linux-gnu/lib/libzerocopy_derive-54d2b38896fa6bc5.so
       = note: candidate #2: .../rust/test/libzerocopy_derive.so

Commit fe39a233ea52 ("rust: kbuild: disambiguate `zerocopy` for
`rusttest`") fixed the equivalent ambiguity for `zerocopy`.

Thus point to the dependency explicitly in this case too.

Cc: Antoni Boucher <[email protected]>
Cc: [email protected]
Fixes: 506054980429 ("rust: zerocopy-derive: enable support in kbuild")
Signed-off-by: Miguel Ojeda <[email protected]>
---
 rust/Makefile | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/rust/Makefile b/rust/Makefile
index fbe0accc51a3..a346a01bb3eb 100644
--- a/rust/Makefile
+++ b/rust/Makefile
@@ -350,7 +350,8 @@ rusttestlib-pin_init: $(src)/pin-init/src/lib.rs rusttestlib-macros \
 rusttestlib-kernel: private rustc_target_flags = --extern ffi \
     --extern build_error --extern macros --extern pin_init \
     --extern bindings --extern uapi \
-    --extern zerocopy=$(objtree)/$(obj)/test/libzerocopy.rlib --extern zerocopy_derive
+    --extern zerocopy=$(objtree)/$(obj)/test/libzerocopy.rlib \
+    --extern zerocopy_derive=$(objtree)/$(obj)/test/libzerocopy_derive.so
 rusttestlib-kernel: $(src)/kernel/lib.rs rusttestlib-bindings rusttestlib-uapi \
     rusttestlib-build_error rusttestlib-pin_init $(obj)/$(libmacros_name) \
     $(obj)/bindings.o rusttestlib-zerocopy rusttestlib-zerocopy_derive FORCE

base-commit: d24f5cdbeff8b6a063fca92d0a1f94122a799b59
-- 
2.55.0