%ghc_gen_filelists: check pkg licensedir exists
prevents warning errors: eg for ghc9.4:
ls: cannot access '~/fedora/haskell/ghc9.4/BUILDROOT/ghc9.4-9.4.0.20220721-7.fc37.x86_64/usr/share/licenses/ghc9.4-Cabal': No such file or directory
etc, though not actually harmful