fix: Copy extra components on darwin

[domwst]

Hi! After updating to a fresh version of rust I've started getting these kinds of errors from rust-lld on macos:

dyld[57979]: Library not loaded: @rpath/libLLVM.dylib
  Referenced from: <1A2A643B-408F-3C7A-B8A2-DC5EDCCD6D11> /nix/store/dsd8a65z7w5dl4i0h8g45qkc2hmk2vva-rustc-1.98.0-nightly-2026-06-02-aarch64-apple-darwin/lib/rustlib/aarch64-apple-darwin/bin/rust-lld
  Reason: tried: '/nix/store/dsd8a65z7w5dl4i0h8g45qkc2hmk2vva-rustc-1.98.0-nightly-2026-06-02-aarch64-apple-darwin/lib/rustlib/aarch64-apple-darwin/bin/../lib/libLLVM.dylib' (no such file), '/Users/runner/work/rust/rust/build/aarch64-apple-darwin/llvm/lib/libLLVM.dylib' (no such file), '/System/Volumes/Preboot/Cryptexes/OS/Users/runner/work/rust/rust/build/aarch64-apple-darwin/llvm/lib/libLLVM.dylib' (no such file), '/nix/store/dsd8a65z7w5dl4i0h8g45qkc2hmk2vva-rustc-1.98.0-nightly-2026-06-02-aarch64-apple-darwin/lib/rustlib/aarch64-apple-darwin/bin/../lib/libLLVM.dylib' (no such file), '/Users/runner/work/rust/rust/build/aarch64-apple-darwin/llvm/lib/libLLVM.dylib' (no such file), '/System/Volumes/Preboot/Cryptexes/OS/Users/runner/work/rust/rust/build/aarch64-apple-darwin/llvm/lib/libLLVM.dylib' (no such file)

It looks like recent versions of helper binaries link dynamically to libLLVM.dylib. The tools live under lib/rustlib/<target>/bin and their rpath include @loader_path/../lib, so dyld expects LLVM at lib/rustlib/<target>/lib/libLLVM.dylib. However, the rustc component provides libLLVM.dylib under: lib/libLLVM.dylib, current fix symlinks the libLLVM.dylib into the corresponding relative path.

This issue was likely triggered by:
rust-lang/rust#157205

There is also
rust-lang/rust#157557
which will likely affect x86_64-darwin as well.

I've tested the fix on aarch64-darwin and x86_64-linux manually (although with llvm-tools-preview component enabled).