perf(x86_64): don't initialize boot stack

Author: mkroening

src/arch/x86_64/stack.rs

@@ -1,14 +1,18 @@
 use core::cell::UnsafeCell;
-use core::mem;
+use core::mem::{self, MaybeUninit};
 
 #[repr(C, align(0x1000))]
-pub struct Stack(UnsafeCell<[u8; 0x1000]>);
+pub struct Stack(UnsafeCell<[MaybeUninit<u8>; 0x1000]>);
 
 unsafe impl Sync for Stack {}
 
 impl Stack {
 	const fn new() -> Self {
-		let fill = 0xcd;
+		let fill = if cfg!(debug_assertions) {
+			MaybeUninit::new(0xcd)
+		} else {
+			MaybeUninit::uninit()
+		};
 		Self(UnsafeCell::new([fill; _]))
 	}