I messed up, I didn't notice that the actual kernel was disabled in
the spec file. I took the source rpm that is being currently built in
koji (4.18.0-0.rc0.git10.1), I removed the nobuildarches macro and the
build failed, albeit at a different step:

Processing /builddir/build/BUILD/kernel-4.17.fc29/linux-4.18.0-0.rc0.git10.1.fc29.i686/configs/kernel-4.18.0-i686-PAE.config
... /builddir/build/BUILD/kernel-4.17.fc29/linux-4.18.0-0.rc0.git10.1.fc29.i686/configs/kernel-4.18.0-i686-PAE.config:5910:warning:
override: UNWINDER_ORC changes choice state
/builddir/build/BUILD/kernel-4.17.fc29/linux-4.18.0-0.rc0.git10.1.fc29.i686/configs/kernel-4.18.0-i686-PAE.config:6381:warning:
override: VIRT_CPU_ACCOUNTING_NATIVE changes choice state
make[1]: *** [scripts/kconfig/Makefile:64: olddefconfig] Segmentation
fault (core dumped)
make: *** [Makefile:536: oldnoconfig] Error 2

Why do we still need the PAE config?
Anyway, sorry to have wasted your time.
If anyone else has any ideas, please chime in.