message: Simplify mock rustc wrapper.
diff: @@ -90,18 +90,7 @@ fn setup() -> Option<Setup> {
  fn main() {
  let mut args = env::args().skip(1).collect::<Vec<_>>();
  - let crates = [
  - "alloc",
  - "compiler_builtins",
  - "core",
  - "panic_unwind",
  - "proc_macro",
  - "std",
  - "test",
  - ];
  - let is_sysroot_crate = args.iter()
  - .any(|a| a.starts_with("rustc_std_workspace") || crates.iter().any(|b| a == b));
  -
  + let is_sysroot_crate = env::var_os("RUSTC_BOOTSTRAP").is_some();
  if is_sysroot_crate {
  let arg = args.iter().position(|a| a == "--sysroot").unwrap();
  args[arg + 1] = env::var("REAL_SYSROOT").unwrap();
  