[Kernel/Threading] Fix some kernel threading issues

- broken atomic exchange on linux
- spinlock release memory buffer
- race in thread suspension
- removed misleading volatile qualifiers

src/xenia/base/threading.h

@@ -83,8 +83,8 @@ class Fence {
   std::mutex mutex_;
   std::condition_variable cond_;
   // Use the highest bit (sign bit) as the signal flag and the rest to count
-  // waiting threads.
-  volatile state_t_ signal_state_;
+  // waiting threads. Protected by mutex_.
+  state_t_ signal_state_;
 };
 
 // Returns the total number of logical processors in the host system.