Also run the bootstrap in bootstrap mode

Author: oli-obk

src/bootstrap/bootstrap.py

@@ -815,6 +815,7 @@ def bootstrap(help_triggered):
     env["BOOTSTRAP_PARENT_ID"] = str(os.getpid())
     env["BOOTSTRAP_PYTHON"] = sys.executable
     env["BUILD_DIR"] = build.build_dir
+    env["RUSTC_BOOTSTRAP"] = '1'
     run(args, env=env, verbose=build.verbose)