Fix the build with memory manager tracing disabled. The guard was missing

in the header.


git-svn-id: file:///srv/svn/repos/haiku/haiku/trunk@43084 a95241bf-73f2-0310-859d-f6bbb57e9c96

src/system/kernel/slab/MemoryManager.h

@@ -60,8 +60,10 @@ public:
 	static	bool				MaintenanceNeeded();
 	static	void				PerformMaintenance();
 
+#if SLAB_MEMORY_MANAGER_ALLOCATION_TRACKING
 	static	bool				AnalyzeAllocationCallers(
 									AllocationTrackingCallback& callback);
+#endif
 
 private:
 			struct Tracing;