Initial process waiting/waking

Processes can now wait on signals/children/time. There is no clock
currently so "time" is just a monotonically increating tick count. Added
a SLEEP syscall to test this waiting/waking.

src/kernel/process.cpp

@@ -0,0 +1,64 @@
+#include "process.h"
+
+
+void
+process::wait_on_signal(uint64_t sigmask)
+{
+	waiting = process_wait::signal;
+	waiting_info = sigmask;
+	flags -= process_flags::ready;
+}
+
+void
+process::wait_on_child(uint32_t pid)
+{
+	waiting = process_wait::child;
+	waiting_info = pid;
+	flags -= process_flags::ready;
+}
+
+void
+process::wait_on_time(uint64_t time)
+{
+	waiting = process_wait::time;
+	waiting_info = time;
+	flags -= process_flags::ready;
+}
+
+bool
+process::wake_on_signal(int signal)
+{
+	if (waiting != process_wait::signal ||
+		(waiting_info & (1 << signal)) == 0)
+		return false;
+
+	waiting = process_wait::none;
+	flags += process_flags::ready;
+	return true;
+}
+
+bool
+process::wake_on_child(process *child)
+{
+	if (waiting != process_wait::child ||
+		(waiting_info && waiting_info != child->pid))
+		return false;
+
+	waiting = process_wait::none;
+	flags += process_flags::ready;
+	return true;
+}
+
+
+bool
+process::wake_on_time(uint64_t now)
+{
+	if (waiting != process_wait::time ||
+		waiting_info > now)
+		return false;
+
+	waiting = process_wait::none;
+	flags += process_flags::ready;
+	return true;
+}
+