So a quick update on where this is.
We've figured out that the issue was caused by an update to the glibc package in the mainline repos. Pinning this back to a known good version allowed us to build working -i686.iso and -dual.iso images. These have been put in the master repo and should be syncing elsewhere shortly.
Let us know if you have any issues with the new archlinux-2017.06.15-*.iso images.