Explicitly instantiate constructors/destructors for Kernel objects

This should speed up compile times a bit, as well as enable more liberal
use of forward declarations. (Due to SharedPtr not trying to emit the
destructor anymore.)

src/core/hle/kernel/thread.cpp

@@ -40,8 +40,8 @@ static Thread* current_thread;
 static const u32 INITIAL_THREAD_ID = 1; ///< The first available thread id at startup
 static u32 next_thread_id; ///< The next available thread id
 
-Thread::Thread() {
-}
+Thread::Thread() {}
+Thread::~Thread() {}
 
 Thread* GetCurrentThread() {
     return current_thread;