tell users how to disable the leak check

Author: RalfJung

src/eval.rs

@@ -302,14 +302,18 @@ pub fn eval_main<'tcx>(tcx: TyCtxt<'tcx>, main_id: DefId, config: MiriConfig) ->
             if !ignore_leaks {
                 // Check for thread leaks.
                 if !ecx.have_all_terminated() {
-                    tcx.sess.err("the main thread terminated without waiting for all remaining threads");
+                    tcx.sess.err(
+                        "the main thread terminated without waiting for all remaining threads",
+                    );
+                    tcx.sess.note_without_error("pass `-Zmiri-ignore-leaks` to disable this check");
                     return None;
                 }
                 // Check for memory leaks.
                 info!("Additonal static roots: {:?}", ecx.machine.static_roots);
                 let leaks = ecx.memory.leak_report(&ecx.machine.static_roots);
                 if leaks != 0 {
                     tcx.sess.err("the evaluated program leaked memory");
+                    tcx.sess.note_without_error("pass `-Zmiri-ignore-leaks` to disable this check");
                     // Ignore the provided return code - let the reported error
                     // determine the return code.
                     return None;