message: dont overwrite bootstrap flags
diff: @@ -381,8 +381,6 @@ path = "lib.rs"
  command.env("RUSTFLAGS", miri::miri_default_args().join(" "));
  command.env("XARGO_HOME", &dir);
  command.env("XARGO_RUST_SRC", &rust_src);
  - // In bootstrap, make sure we don't get debug assertons into our libstd.
  - command.env("RUSTC_DEBUG_ASSERTIONS", "false");
  // Handle target flag.
  if let Some(ref target) = target {
  command.arg("--target").arg(&target);
  