support packaging Cabal bundled internal libraries
    
    for some reason installing with Cabal (rather than cabal-install)
    gives different hashes for the sublibrary
    
    simplification of initial work in opensuse by Ondřej Súkup
    https://github.com/fedora-haskell/ghc-rpm-macros/pull/7
    
    testcase was haddock-library-1.4.5