Do not report overflow error.

Author: cjgillot

compiler/rustc_trait_selection/src/traits/mod.rs

@@ -432,6 +432,9 @@ pub fn impossible_predicates<'tcx>(
     debug!("impossible_predicates(predicates={:?})", predicates);
 
     let result = tcx.infer_ctxt().enter(|infcx| {
+        // HACK: Set tainted by errors to gracefully exit in case of overflow.
+        infcx.set_tainted_by_errors();
+
         let param_env = ty::ParamEnv::reveal_all();
         let mut selcx = SelectionContext::new(&infcx);
         let mut fulfill_cx = FulfillmentContext::new();