After consulting with Jakub, I switched rawhide to generic GCC tuning on i686, as was the intent when we dropped the Atom tuning for Fedora 26.
See: https://bugzilla.redhat.com/show_bug.cgi?id=1538693
This should paper over most instances of the compiler bug in question. (GCC itself has been built with generic tuning, adding a fair amount of coverage testing.)
This should unblock rawhide development again.
Thanks, Florian