Disable non-functional ppc64 support for ldc packages
    
    Sadly, ldc ppc64 support has detoriated so much that it no longer works
    with any current llvm version. I'll keep an eye on things and re-enable
    it once it's fixed, but right now it's just broken and upstream is
    suggesting to disable the support for now.
    
    https://github.com/ldc-developers/ldc/issues/2356