Specify output directory for bootstrap tests

src/bootstrap/builder/tests.rs

@@ -10,6 +10,9 @@ fn configure(cmd: &str, host: &[&str], target: &[&str]) -> Config {
     config.dry_run = true;
     config.ninja_in_file = false;
     // try to avoid spurious failures in dist where we create/delete each others file
+    config.out = PathBuf::from(env::var_os("BOOTSTRAP_OUTPUT_DIRECTORY").unwrap());
+    config.initial_rustc = PathBuf::from(env::var_os("RUSTC").unwrap());
+    config.initial_cargo = PathBuf::from(env::var_os("BOOTSTRAP_INITIAL_CARGO").unwrap());
     let dir = config
         .out
         .join("tmp-rustbuild-tests")

src/bootstrap/test.rs

@@ -2024,6 +2024,8 @@ fn run(self, builder: &Builder<'_>) {
             .current_dir(builder.src.join("src/bootstrap"))
             .env("RUSTFLAGS", "-Cdebuginfo=2")
             .env("CARGO_TARGET_DIR", builder.out.join("bootstrap"))
+            .env("BOOTSTRAP_OUTPUT_DIRECTORY", &builder.config.out)
+            .env("BOOTSTRAP_INITIAL_CARGO", &builder.config.initial_cargo)
             .env("RUSTC_BOOTSTRAP", "1")
             .env("RUSTC", &builder.initial_rustc);
         if let Some(flags) = option_env!("RUSTFLAGS") {