Derive traversable impls for BindingForm

BindingForm has been a no-op traversable ever since it was first added
in cac6126, but it was modified in 0193d1f to (optionally) contain a
Place without its implementations being updated to fold/visit such.

By using the derive macro to implement the visitable traits, we ensure
that all contained types of interest are folded/visited.

Author: eggyal

Diff for: compiler/rustc_middle/src/mir/mod.rs

@@ -674,7 +674,7 @@ pub enum LocalKind {
     ReturnPointer,
 }
 
-#[derive(Clone, Debug, TyEncodable, TyDecodable, HashStable)]
+#[derive(Clone, Debug, TyEncodable, TyDecodable, HashStable, TypeFoldable, TypeVisitable)]
 pub struct VarBindingForm<'tcx> {
     /// Is variable bound via `x`, `mut x`, `ref x`, or `ref mut x`?
     pub binding_mode: ty::BindingMode,
@@ -696,7 +696,7 @@ pub struct VarBindingForm<'tcx> {
     pub pat_span: Span,
 }
 
-#[derive(Clone, Debug, TyEncodable, TyDecodable)]
+#[derive(Clone, Debug, TyEncodable, TyDecodable, TypeFoldable, TypeVisitable)]
 pub enum BindingForm<'tcx> {
     /// This is a binding for a non-`self` binding, or a `self` that has an explicit type.
     Var(VarBindingForm<'tcx>),
@@ -706,7 +706,7 @@ pub enum BindingForm<'tcx> {
     RefForGuard,
 }
 
-TrivialTypeTraversalAndLiftImpls! {
+CloneLiftImpls! {
     for<'tcx> {
         BindingForm<'tcx>,
     }