libkernel: waker_set: return whether a waker was woken

Make `wake_one()` return `true` indicating whether a waker was woken
from the set, `false` otherwise.

libkernel/src/sync/condvar.rs

@@ -51,7 +51,9 @@ impl<S, C: CpuOps> CondVar<S, C> {
 
         match updater(&mut inner.state) {
             WakeupType::None => (),
-            WakeupType::One => inner.wakers.wake_one(),
+            WakeupType::One => {
+                inner.wakers.wake_one();
+            }
             WakeupType::All => inner.wakers.wake_all(),
         }
     }

libkernel/src/sync/waker_set.rs

@@ -54,9 +54,14 @@ impl WakerSet {
     }
 
     /// Wakes one waiting task, if any.
-    pub fn wake_one(&mut self) {
+    ///
+    /// Returns `true` if a waker was awoken, `false` otherwise.
+    pub fn wake_one(&mut self) -> bool {
         if let Some((_, waker)) = self.waiters.pop_first() {
             waker.wake();
+            true
+        } else {
+            false
         }
     }