Fixes warning: ``` ../Source/UnitTests/Core/CoreTimingTest.cpp: In function 'void AdvanceAndCheck(u32, int, int, int)': ../Source/UnitTests/Core/CoreTimingTest.cpp:52:6: error: no previous declaration for 'void AdvanceAndCheck(u32, int, int, int)' [-Werror=missing-declarations] void AdvanceAndCheck(u32 idx, int downcount, int expected_lateness = 0, int cpu_downcount = 0) ^ ```
The min-heap provides no ordering when the key is the same on 2 nodes. Disambiguate identical times by tracking the order items were added into the queue.
ForceExceptionCheck messes up the downcount and slice length if the callback is scheduled into the past (g_slice_length becomes negative)