message: Fix tests not working with a different CARGO_TARGET_DIR.
diff: use cargo_test_support::registry::{Dependency, Package};
  use cargo_test_support::ProjectBuilder;
  use cargo_test_support::{is_nightly, paths, project, rustc_host, Execs};
  -use std::path::PathBuf;
  +use std::path::{Path, PathBuf};
  struct Setup {
  rustc_wrapper: PathBuf,
  @@ -131,15 +131,7 @@ fn setup() -> Option<Setup> {
  fn enable_build_std(e: &mut Execs, setup: &Setup) {
  // First up, force Cargo to use our "mock sysroot" which mimics what
  // libstd looks like upstream.
  - let root = paths::root();
  - let root = root
  - .parent() // chop off test name
  - .unwrap()
  - .parent() // chop off `citN`
  - .unwrap()
  - .parent() // chop off `target`
  - .unwrap()
  - .join("tests/testsuite/mock-std");
  + let root = Path::new(env!("CARGO_MANIFEST_DIR")).join("tests/testsuite/mock-std");
  e.env("__CARGO_TESTS_ONLY_SRC_ROOT", &root);
  e.masquerade_as_nightly_cargo();
  