This makes the code shorter and clearer.
The only incompatible change is that an explicit command-line argument
`--crates-toml=` will take precedence over the `LINTCHECK_TOML`
environment variable.
Using `rayon::current_num_threads()` causes a bug:
```
thread 'main' panicked at 'called `Result::unwrap()` on an `Err` value:
ThreadPoolBuildError { kind: GlobalPoolAlreadyInitialized }',
src/main.rs:632:10
```
Moreover, using the number of threads and dividing it by 2 wouldn't
return the number of physical threads on modern processors which have
a varying number of threads per core.
It makes little sense to restrict ourselves to physical threads,
especially when, in modern architectures, cores with multiple threads
are often faster (performance) while cores with a unique threads are
often slower (efficient). The Rust runtime will make a better choice.
Causes cargo to re-run clippy when those paths are modified
Also tracks the path to `clippy-driver` in debug mode to remove the
workarounds in `cargo dev lint` and `lintcheck`
This has been unstable since it was first introduced in
https://github.com/rust-lang/rust-clippy/pull/5363. In that time, I have
been using it successfully in nightly without issues. I don't think
there are any blocking issues now that RUSTC_WORKSPACE_WRAPPER is
stabilized, so this can be stabilized.
This will terminate the program if run via "cargo run".
"cargo run" does currently not work because at least a bunch of paths do not take that into account.
