Help diagnosing libtorrent build test failure on ppc64el

Hi.

I'm trying to update libtorrent (and thus rtorrent) in unstable to 
something a bit more recent. I've taken the latest stable release 
(0.15.7) and done an upload to experimental. It turns out this now hits 
a build time test failure on ppc64el, while still building successfully 
on all other release platforms.

Looking at the tests it's the 
torrent/utils::TestSignalInterrupt::test_thread_interrupt test that's 
failing, which appears to be trying to do signal delivery to a C++ 
thread and confirm it behaves as expected.

AFAICT the test that's failing is:

https://salsa.debian.org/debian/libtorrent/-/blob/master/test/torrent/utils/test_signal_interrupt.cc?ref_type=heads#L72

build log of the failure:

https://buildd.debian.org/status/fetch.php?pkg=libtorrent&arch=ppc64el&ver=0.15.7-1&stamp=1765206808&raw=0

My PPC / C++ knowledge is weak here, but this feel like it's potentially 
just a racy test? I see a commit a while back that says "Add more 
lenancy to thread signal interrupt unit test." but actually seems to be 
changing the test_hammer() test.

Upstream, should this just be loosened? Debian PPC gurus, is there 
anything odd with PPC that might be a reason here that needs a specific 
PPC fix?

J.