[util] Add move-assignment operators to node_map, deque

Also add them to wait_queue as a wrapper to calling deque's
move-assignmen operator.

src/kernel/wait_queue.cpp

@@ -1,8 +1,20 @@
+#include <utility>
 #include "objects/thread.h"
 #include "wait_queue.h"
 
+wait_queue::wait_queue(wait_queue &&other) :
+    m_threads {std::move(other.m_threads)} {}
+
 wait_queue::~wait_queue() { clear(); }
 
+wait_queue &
+wait_queue::operator=(wait_queue &&other)
+{
+    clear();
+    m_threads = std::move(other.m_threads);
+    return *this;
+}
+
 void
 wait_queue::add_thread(obj::thread *t)
 {

src/kernel/wait_queue.h

@@ -12,6 +12,11 @@ namespace obj {
 class wait_queue
 {
 public:
+    wait_queue() = default;
+    wait_queue(wait_queue &&other);
+
+    wait_queue & operator=(wait_queue &&other);
+
     /// Wake all threads when destructing
     ~wait_queue();
 
@@ -28,6 +33,9 @@ public:
     /// \arg value  The value passed to thread::wake
     void clear(uint64_t value = 0);
 
+    /// Check if the queue is empty
+    bool empty() const { return m_threads.empty(); }
+
 private:
     /// Get rid of any exited threads that are next
     /// in the queue. Caller must hold the queue lock.