rustc_const_eval: adopt let else in more places

compiler/rustc_const_eval/src/const_eval/eval_queries.rs

@@ -231,9 +231,8 @@ pub fn eval_to_const_value_raw_provider<'tcx>(
     // Catch such calls and evaluate them instead of trying to load a constant's MIR.
     if let ty::InstanceDef::Intrinsic(def_id) = key.value.instance.def {
         let ty = key.value.instance.ty(tcx, key.param_env);
-        let substs = match ty.kind() {
-            ty::FnDef(_, substs) => substs,
-            _ => bug!("intrinsic with type {:?}", ty),
+        let ty::FnDef(_, substs) = ty.kind() else {
+            bug!("intrinsic with type {:?}", ty);
         };
         return eval_nullary_intrinsic(tcx, key.param_env, def_id, substs).map_err(|error| {
             let span = tcx.def_span(def_id);

compiler/rustc_const_eval/src/const_eval/machine.rs

@@ -318,15 +318,12 @@ impl<'mir, 'tcx> interpret::Machine<'mir, 'tcx> for CompileTimeInterpreter<'mir,
         let intrinsic_name = ecx.tcx.item_name(instance.def_id());
 
         // CTFE-specific intrinsics.
-        let (dest, ret) = match ret {
-            None => {
-                return Err(ConstEvalErrKind::NeedsRfc(format!(
-                    "calling intrinsic `{}`",
-                    intrinsic_name
-                ))
-                .into());
-            }
-            Some(p) => p,
+        let Some((dest, ret)) = ret else {
+            return Err(ConstEvalErrKind::NeedsRfc(format!(
+                "calling intrinsic `{}`",
+                intrinsic_name
+            ))
+            .into());
         };
         match intrinsic_name {
             sym::ptr_guaranteed_eq | sym::ptr_guaranteed_ne => {