[kernel] Add object_wait_many syscall

Add the object_wait_many syscall to allow programs to wait for signals
on multiple objects at once. Also removed the object argument to
thread::wait_on_signals, which does nothing with it. That information is
saved in the thread being in the object's blocked threads list.

src/kernel/objects/kobject.cpp

@@ -50,13 +50,11 @@ void
 kobject::notify_signal_observers()
 {
 	size_t i = 0;
-	bool readied = false;
 	while (i < m_blocked_threads.count()) {
 		thread *t = m_blocked_threads[i];
 
 		if (t->wake_on_signals(this, m_signals)) {
 			m_blocked_threads.remove_swap_at(i);
-			readied = true;
 		} else {
 			++i;
 		}

src/kernel/objects/thread.cpp

@@ -48,7 +48,7 @@ thread & thread::current() { return *current_cpu().thread; }
 inline void schedule_if_current(thread *t) { if (t == current_cpu().thread) scheduler::get().schedule(); }
 
 void
-thread::wait_on_signals(kobject *obj, j6_signal_t signals)
+thread::wait_on_signals(j6_signal_t signals)
 {
 	m_wait_type = wait_type::signal;
 	m_wait_data = signals;

src/kernel/objects/thread.h

@@ -74,10 +74,9 @@ public:
 	/// \arg p  The new thread priority
 	inline void set_priority(uint8_t p) { if (!constant()) m_tcb.priority = p; }
 
-	/// Block the thread, waiting on the given object's signals.
-	/// \arg obj     Object to wait on
+	/// Block the thread, waiting an object's signals.
 	/// \arg signals Mask of signals to wait for
-	void wait_on_signals(kobject *obj, j6_signal_t signals);
+	void wait_on_signals(j6_signal_t signals);
 
 	/// Block the thread, waiting for a given clock value
 	/// \arg t  Clock value to wait for
@@ -114,6 +113,9 @@ public:
 	/// Get the current blocking opreation's wait data
 	uint64_t get_wait_data() const { return m_wait_data; }
 
+    /// Get the current blocking operation's wait ojbect (as a handle)
+	j6_koid_t get_wait_object() const { return m_wait_obj; }
+
 	inline bool has_state(state s) const {
 		return static_cast<uint8_t>(m_state) & static_cast<uint8_t>(s);
 	}