The kernel's spec file contains this line:
The (minor) problem with this is that with RPM spec files, one should be able to build the source RPM in a reproduceable way whatever the build system's arch, or as noarch. I'm talking about the source RPM only, not the binary RPM that obviously needs to depend on the arch.
Here's what happens if you try to build the source RPM with `rpmbuild -bs --target noarch`:
Actually, the way Source1 is defined wouldn't even work if there were multiple supported arches for the kernel, because you would get specific versions of the source RPM depending on the target arch, which defeats the purpose of source RPMs. If you really needed to build for separate arches with separate kernel configurations, then you would have to define several SourceX and use the appropriate one depending on the build arch.
Suggestion: simply define it as: