clippy: fix on darwin

As of Rust 1.67.0, the cargo-clippy binary now relies on the rustc_private
libraries [0], so let's do the RPATH fixup to it too.

I've also added a comment to explain the RPATH situation, as it took me
a bit to figure out.

[0]: rust-lang/rust-clippy#9541

pkgs/development/compilers/rust/clippy.nix

@@ -20,8 +20,15 @@ rustPlatform.buildRustPackage {
   #   (/private/tmp/nix-build-clippy-1.36.0.drv-0/rustc-1.36.0-src/src/librustc_llvm)
   doCheck = false;
 
+  # Clippy uses the rustc_driver and std private libraries, and Rust's build process forces them to have
+  # an install name of `@rpath/...` [0] [1] instead of the standard on macOS, which is an absolute path
+  # to itself.
+  #
+  # [0]: https://github.com/rust-lang/rust/blob/f77f4d55bdf9d8955d3292f709bd9830c2fdeca5/src/bootstrap/builder.rs#L1543
+  # [1]: https://github.com/rust-lang/rust/blob/f77f4d55bdf9d8955d3292f709bd9830c2fdeca5/compiler/rustc_codegen_ssa/src/back/linker.rs#L323-L331
   preFixup = lib.optionalString stdenv.isDarwin ''
-    install_name_tool -add_rpath "${rustc}/lib" $out/bin/clippy-driver
+    install_name_tool -add_rpath "${rustc}/lib" "$out/bin/clippy-driver"
+    install_name_tool -add_rpath "${rustc}/lib" "$out/bin/cargo-clippy"
   '';
 
   meta = with lib; {