message: use rustc_version also to parse host in compiletest
diff: @@ -142,17 +142,15 @@ fn get_sysroot() -> PathBuf {
  fn get_host() -> String {
  let rustc = rustc_test_suite().unwrap_or(PathBuf::from("rustc"));
  - let host = std::process::Command::new(rustc)
  + let rustc_version = std::process::Command::new(rustc)
  .arg("-vV")
  .output()
  .expect("rustc not found for -vV")
  .stdout;
  - let host = std::str::from_utf8(&host).expect("sysroot is not utf8");
  - let host = host.split("\nhost: ").nth(1).expect(
  - "no host: part in rustc -vV",
  - );
  - let host = host.split('\n').next().expect("no \n after host");
  - String::from(host)
  + let rustc_version = std::str::from_utf8(&rustc_version).expect("rustc -vV is not utf8");
  + let version_meta = rustc_version::version_meta_for(&rustc_version)
  + .expect("failed to parse rustc version info");
  + version_meta.host
  }
  fn run_pass_miri(opt: bool) {
  