I started looking into it, but quickly found that all or almost all the failures are all due to the rpm upgrade, and the failures all happen on three old distros: centos 7, debian 8, ubuntu 16.04.
What is particularly odd is that the centos/debian failures are non-deterministic: in some cases rpm-native fails to build due to missing omp.h, in other cases it builds, but the resulting binaries segfault. This non-determinism seems to happen even on the same worker, e.g.:
(one is failing in do_compile, another compiles fine, but then produces segfaults)
Ubuntu always segfaults, but maybe it's just coincidental.
I am not sure how to take this further, but maybe the best course of action is to defer the rpm/dnf update once more, until those old distros are finally retired.
Alex