Is threads on s390x different from other architectures?

I have a build failure on s390x which made me wonder.  The trouble is
with the self test, which is failing on all archs (probably because of
$HOME not being writable, fixing in the next uplad).  Because the tests
are failing, I made failing tests non-fatal (using '-dh_auto_test' in
rules).  This get the build limping along on all architectures except
s390x, where the build hack forever and is killed after 150 minutes.

Any of you have any idea why the threads on s390x behave differently
than all the other architectures?

The package in question is
<URL: https://tracker.debian.org/pkg/vlc-plugin-bittorrent >.