Make sure backtrace printed by STW straggler goes into safe-log-file

[d-netto]

PR Description

MWE:

function main()
    t = Threads.@spawn begin
        ccall(:uv_sleep, Cvoid, (Cuint,), 5000)
    end
    # Force a GC
    ccall(:uv_sleep, Cvoid, (Cuint,), 1000)
    GC.gc()
    wait(t)
end
main()

Command:

julia -t4 --timeout-for-safepoint-straggler=1 --safe-crash-log-file=/tmp/foobar.txt mwe.jl

Output:

Ran:

cat /tmp/foobar.txt 

And got:

{"level":"Error", "timestamp":"2025-02-04T18:27:20.513", "message": "===== Thread 2 failed to reach safepoint after 1 seconds, printing backtrace below =====\n"}

{"level":"Error", "timestamp":"2025-02-04T18:27:20.651", "message": "thread (1) __semwait_signal at /usr/lib/system/libsystem_kernel.dylib (unknown line)\n"}

{"level":"Error", "timestamp":"2025-02-04T18:27:21.651", "message": "===== Thread 2 failed to reach safepoint after 1 seconds, printing backtrace below =====\n"}

{"level":"Error", "timestamp":"2025-02-04T18:27:21.652", "message": "thread (1) __semwait_signal at /usr/lib/system/libsystem_kernel.dylib (unknown line)\n"}

{"level":"Error", "timestamp":"2025-02-04T18:27:22.652", "message": "===== Thread 2 failed to reach safepoint after 1 seconds, printing backtrace below =====\n"}

{"level":"Error", "timestamp":"2025-02-04T18:27:22.652", "message": "thread (1) __semwait_signal at /usr/lib/system/libsystem_kernel.dylib (unknown line)\n"}

Checklist

Requirements for merging:

• I have opened an issue or PR upstream on JuliaLang/julia: N/A.
• I have removed the port-to-* labels that don't apply.
• I have opened a PR on raicode to test these changes: