Avoid setting annobin flags if !_annotated_build
    
    Without this, the glibc build fails if annobin hasn't been bootstrapped
    against an updated gcc major version.  This will likely never happen in
    production builds since _annotated_build is always set through
    redhat-rpm-config but when testing with annobin disabled (*and* with a
    rebased gcc), it may end up unnecessarily making gcc look for annobin.