Recover when failing to normalize closure signature.

src/base.rs

@@ -686,6 +686,7 @@ fn is_fat_ptr<'tcx>(fx: &FunctionCx<'_, '_, 'tcx>, ty: Ty<'tcx>) -> bool {
                                 substs,
                                 ty::ClosureKind::FnOnce,
                             )
+                            .expect("failed to normalize and resolve closure during codegen")
                             .polymorphize(fx.tcx);
                             let func_ref = fx.get_function_ref(instance);
                             let func_addr = fx.bcx.ins().func_addr(fx.pointer_type, func_ref);