lxc-based builders seem not to have lxcfs enabled
Under lxc, side-effects can happen when resources are limited.
As an example, see https://build.alpinelinux.org/buildlogs/build-edge-x86/community/caddy/caddy-1.0.0-r0.log
This is caused by the container not knowing what it’s actually allowed to use, and thus not having a value (in this case, defaulting to –1).
This can and will cause various failures.
(from redmine: issue id 10484, created on 2019-05-23)