Store stack in a box

Summary:
Need to make stack resizable.

Resizable means extra indirection.

Add indirection now to check there's no perf regression.

Reviewed By: JakobDegen

Differential Revision: D48955721

fbshipit-source-id: 2769d2845839f00af2c08f707434c55423ed9538

Author: stepancheg

starlark/src/eval/runtime/cheap_call_stack.rs

@@ -82,17 +82,19 @@ enum CallStackError {
 #[derive(Debug)]
 pub(crate) struct CheapCallStack<'v> {
     count: usize,
-    stack: [CheapFrame<'v>; MAX_CALLSTACK_RECURSION],
+    stack: Box<[CheapFrame<'v>; MAX_CALLSTACK_RECURSION]>,
 }
 
 impl<'v> Default for CheapCallStack<'v> {
     fn default() -> Self {
         Self {
             count: 0,
-            stack: [CheapFrame {
-                function: Value::new_none(),
-                span: None,
-            }; MAX_CALLSTACK_RECURSION],
+            stack: Box::new(
+                [CheapFrame {
+                    function: Value::new_none(),
+                    span: None,
+                }; MAX_CALLSTACK_RECURSION],
+            ),
         }
     }
 }