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