I've captured an [strace log](https://gist.github.com/508e07e299f05f81f928eb187b6a69ff) from re-running `xbps-install -Su`.
As can be seen from the log, I have several local repositories enabled, pointing into `~/void-packages/hostdir/binpkgs/*` directories, and I haven't had any problems with installing locally-built packages from these repositories in the past.