I tried cross-building it in the latest mock (1.4.11-1), with
mock -r fedora-29-i386 --forcearch=i386 kernel-4.18.0-0.rc0.git9.1.fc29.src.rpm
and it failed right after installing repos and keys:
Finish: dnf install
Config(fedora-rawhide-i386) 1 minutes 16 seconds
INFO: Results and/or logs in: /var/lib/mock/fedora-rawhide-i386/result
ERROR: Could not find useradd in chroot, maybe the install failed?
The logs don't mention something useful, and I won't be able to test
on actual 32-bit hardware until later tonight.