message: Don't set RUSTC_WRAPPER if not configured
diff: @@ -250,10 +250,9 @@ fn build_work(cx: &mut Context<'_, '_>, unit: &Unit) -> CargoResult<Job> {
  }
  // Also inform the build script of the rustc compiler context.
  - cmd.env(
  - "CARGO_RUSTC_WRAPPER",
  - bcx.rustc().wrapper.as_deref().unwrap_or(Path::new("")),
  - );
  + if let Some(wrapper) = bcx.rustc().wrapper.as_ref() {
  + cmd.env("CARGO_RUSTC_WRAPPER", wrapper);
  + }
  cmd.env("CARGO_RUSTFLAGS", bcx.rustflags_args(unit).join(" "));
  // Gather the set of native dependencies that this package has along with
  