Fix i686 using cmpxchg8b-based AtomicU64 for stats.

src/cpu_stats.rs

@@ -1,5 +1,13 @@
 use alloc::{string::String, vec::Vec};
-use core::sync::atomic::{AtomicU64, AtomicU8, AtomicUsize, Ordering};
+
+// implemented using cmpxchg8b
+#[cfg(target_arch = "x86")]
+use syscall::sigabi::AtomicU64;
+
+#[cfg(not(target_arch = "x86"))]
+use core::sync::atomic::AtomicU64;
+
+use core::sync::atomic::{AtomicU8, AtomicUsize, Ordering};
 
 use crate::cpu_set::LogicalCpuId;