make the instancetracker unit test really, like, work. before I fiddle with a big pile of stuff.

indra/llcommon/CMakeLists.txt

@@ -165,7 +165,6 @@ set(llcommon_HEADER_FILES
     llhttpstatuscodes.h
     llindexedqueue.h
     llinstancetracker.h
-    llinstancetracker.h
     llkeythrottle.h
     lllazy.h
     lllistenerwrapper.h

indra/llcommon/llinstancetracker.cpp

@@ -0,0 +1,20 @@
+/**
+ * @file   lllinstancetracker.cpp
+ * 
+ * $LicenseInfo:firstyear=2009&license=viewergpl$
+ * Copyright (c) 2009, Linden Research, Inc.
+ * $/LicenseInfo$
+ */
+
+// Precompiled header
+#include "linden_common.h"
+// associated header
+#include "llinstancetracker.h"
+// STL headers
+// std headers
+// external library headers
+// other Linden headers
+
+// llinstancetracker.h is presently header-only. This file exists only because our CMake
+// test macro ADD_BUILD_TEST requires it.
+int dummy = 0;