BR: ExtUtils::CBuilder
    
    - Arch-specific package using Module::Build needs to use ExtUtils::CBuilder
      (https://bugzilla.redhat.com/show_bug.cgi?id=1547165#c7)
    - Drop explicit gcc build-require as EU::CB is effectively our compiler here
    - Add build-require coreutils for %{_fixperms}
    - Simplify find command using -empty