For a mock build, isa is probably not useful. But for people who still use just rpmbuild, and multilib, it's easy to get screwed without isa in BuildRequires (or at least it'd seem that you'd want it, if you didn't check what actually happened).
For a mock build, isa is probably not useful. But for people who still use just rpmbuild, and multilib, it's easy to get screwed without isa in BuildRequires (or at least it'd seem that you'd want it, if you didn't check what actually happened).