It turns out the reason yaz4 was segfaulting in libgnutls.so.26 is because we were pointing at an HTTPS URL for SRU; if you point at a plain old HTTP URL for SRU, then yaz4 works just fine. A bit problematic if your site is HTTPS everywhere, but this is hopefully helpful for anyone looking to reproduce the symptoms.
It turns out the reason yaz4 was segfaulting in libgnutls.so.26 is because we were pointing at an HTTPS URL for SRU; if you point at a plain old HTTP URL for SRU, then yaz4 works just fine. A bit problematic if your site is HTTPS everywhere, but this is hopefully helpful for anyone looking to reproduce the symptoms.