message: Wrap an error context for determining the amount of parallelism
diff: use crate::core::compiler::CompileKind;
  use crate::util::interning::InternedString;
  use crate::util::{CargoResult, Config, RustfixDiagnosticServer};
  -use anyhow::bail;
  +use anyhow::{bail, Context as _};
  use cargo_util::ProcessBuilder;
  use serde::ser;
  use std::cell::RefCell;
  @@ -73,7 +73,9 @@ impl BuildConfig {
  }
  let jobs = match jobs.or(cfg.jobs) {
  Some(j) => j,
  - None => available_parallelism()?.get() as u32,
  + None => available_parallelism()
  + .context("failed to determine the amount of parallelism available")?
  + .get() as u32,
  };
  if jobs == 0 {
  anyhow::bail!("jobs may not be 0");
  