make tests pass again

src/bin/miri.rs

@@ -1,5 +1,9 @@
 #![feature(rustc_private, stmt_expr_attributes)]
-#![allow(clippy::manual_range_contains, clippy::useless_format)]
+#![allow(
+    clippy::manual_range_contains,
+    clippy::useless_format,
+    clippy::field_reassign_with_default
+)]
 
 extern crate rustc_data_structures;
 extern crate rustc_driver;

tests/pass/backtrace/backtrace-global-alloc.rs

@@ -1,4 +1,5 @@
 //@compile-flags: -Zmiri-disable-isolation
+//@rustc-env: RUST_BACKTRACE=1
 
 #![feature(backtrace)]
 

tests/pass/backtrace/backtrace-std.rs

@@ -1,4 +1,5 @@
 //@compile-flags: -Zmiri-disable-isolation
+//@rustc-env: RUST_BACKTRACE=1
 
 #![feature(backtrace)]