box_free_worker: Pull out version that just borrows alloc

Author: Ericson2314

src/liballoc/alloc.rs

@@ -229,10 +229,15 @@ type BoxFreeAlloc<A> = A;
 
 #[cfg_attr(not(test), lang = "box_free")]
 #[inline]
-pub(crate) unsafe fn box_free<T: ?Sized, A: Stage0Alloc>(ptr: Unique<T>, a: BoxFreeAlloc<A>) {
+pub(crate) unsafe fn box_free<T: ?Sized, A: Alloc>(ptr: Unique<T>, mut a: BoxFreeAlloc<A>) {
+    box_free_worker(ptr, &mut a)
+}
+
+#[inline]
+pub(crate) unsafe fn box_free_worker<T: ?Sized, A: Alloc>(ptr: Unique<T>, a: &mut BoxFreeAlloc<A>) {
     let size = size_of_val(&*ptr.as_ptr());
     let align = min_align_of_val(&*ptr.as_ptr());
-    // We do not allocate for Box<T, A> when T is ZST, so deallocation is also not necessary.
+    // We do not allocate for Box<T> when T is ZST, so deallocation is also not necessary.
     if size != 0 {
         let layout = Layout::from_size_align_unchecked(size, align);
         stage0_unphantom(a).dealloc(NonNull::from(ptr).cast(), layout);