Forward -B linker search path in thin/patch link args on Linux

[Wilovy09]

Since Rust 1.86, the toolchain injects two flags when linking on Linux to use the bundled lld instead of the system ld:

• B/path/to/rustup/.../gcc-ld — tells cc where to find linker programs
• fuse-ld=lld — tells cc to select lld

The fat link captures the full set of args from the initial cargo build and replays them verbatim, so it already picked up both flags and worked correctly on systems without binutils installed.

The patch link (thin) builds its own arg list in thin_link_args. It forwarded -fuse-ld but not -B, so cc -fuse-ld=lld could not locate ld.lld from the Rust toolchain and fell back to the system ld, failing with:

collect2: fatal error: cannot find 'ld'

Fix: add -B to the pass-through filter so the patch linker invocation forwards the same gcc-ld search path that cargo injects.

Implementation notes - Rust RFC

On the x86_64-unknown-linux-gnu target, when using the default linker flavor (using cc as the linker driver) and linker features (to try using lld), rustc will try to use the self-contained linker by passing a -B /path/to/sysroot/ link argument to the driver to find rust-lld in the sysroot. For backwards-compatibility, and to limit name and PATH collisions, this is done using a shim executable (the lld-wrapper tool) that forwards execution to the rust-lld executable itself.

Thanks to:

• @marc2332 , for testing on Ubuntu 24.04 with Rust 1.94
• @SergioRibera , for testing on NixOS 26.03
• @MarioYellowy , for testing on PopOS 24.04 with Rust 1.94.1
  I tested it on MacOS 23.3.1(a) with Rust 1.93

[Wilovy09]

@jkelleyrtp formatted!

[jkelleyrtp]

Thanks!!