Export GetInvalidThreadID() through RageThreads.h, rather than arch/Threads/Thread.h (via GetInvalidThreadId(), lowercase d).

stepmania/src/RageThreads.cpp

@@ -360,6 +360,10 @@ uint64_t RageThread::GetCurrentThreadID()
 {
 	return GetThisThreadId();
 }
+uint64_t RageThread::GetInvalidThreadID()
+{
+	return GetInvalidThreadId();
+}
 
 /* Normally, checkpoints are only seen in crash logs.  It's occasionally useful
  * to see them in logs, but this outputs a huge amount of text. */

stepmania/src/RageThreads.h

@@ -39,6 +39,7 @@ public:
 
 	static bool GetIsShowingDialog() { return s_bIsShowingDialog; }
 	static void SetIsShowingDialog( bool b ) { s_bIsShowingDialog = b; }
+	static uint64_t GetInvalidThreadID();
 
 private:
 	ThreadSlot *m_pSlot;