HANG tool.drcachesim.phys-threads once on GA CI

The new tool.drcachesim.phys-threads test failed once in a PR with a hang:

https://github.com/DynamoRIO/dynamorio/runs/6716249823?check_suite_focus=true
```
] 90.00 sec

-------------------------------------------------------------------
Performance for solving AX=B Linear Equation using Jacobi method
Running on DynamoRIO
Client version (null)
...................................................................

Matrix Size : 64
Threads : 4
```

Stopping at that early point in the output and then timing out sure looks like a hang.

Happened just the once.