Add super_local method to the MIR visitors.

`visit_local` is the only method that doesn't call a corresponding
`super_local` method. This is valid, because `super_local` would be
empty. But it's inconsistent with every other case; we have multiple
other empty `super` methods: `super_span`, `super_ty`, etc.

This commit adds an empty `super_local` and makes `visit_local` call it.

Author: nnethercote

compiler/rustc_middle/src/mir/visit.rs

@@ -270,10 +270,12 @@ macro_rules! make_mir_visitor {
 
             fn visit_local(
                 &mut self,
-                _local: $(& $mutability)? Local,
-                _context: PlaceContext,
-                _location: Location,
-            ) {}
+                local: $(& $mutability)? Local,
+                context: PlaceContext,
+                location: Location,
+            ) {
+                self.super_local(local, context, location)
+            }
 
             fn visit_source_scope(
                 &mut self,
@@ -868,6 +870,14 @@ macro_rules! make_mir_visitor {
                 }
             }
 
+            fn super_local(
+                &mut self,
+                _local: $(& $mutability)? Local,
+                _context: PlaceContext,
+                _location: Location,
+            ) {
+            }
+
             fn super_var_debug_info(
                 &mut self,
                 var_debug_info: & $($mutability)? VarDebugInfo<'tcx>