Test case backtraces report stack from wrong threads

[cujomalainey]

I am seeing a few reports in sound-open-firmware where the stack trace points to a crash in pthread_create but when I reproduce in lldb it points to a proper location in the code base. This is fine for reliable test cases but for unreliable ones this is problematic as the automated backtraces are the main source of information for debugging.

Example test cases
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