Auto merge of #74578 - ehuss:fix-rust-src, r=Mark-Simulacrum

Fix rust-src component.

The rust-src component could not be installed by rustup because it included some symbolic links. #74520 added the backtrace directory which included some symlinks. Since the rust-src component doesn't need most of the files in the `backtrace` submodule, this changes it to only include the minimum necessary.

Tested with cargo's build-std that it can build from the resulting tarball.

Fixes #74577