This hasn't been an issue on x86_64, but running it anyways shouldn't
hurt. aarch64-darwin's trouble could be due to codesigning? Besides that
there don't seem to be many differences between the actual derivations.
This also unbreaks the test suite of regex-rure.
Also regenerate hackage-packages.nix so it picks up on the newly added
library and remove the broken flag no haskell.packages.ghc921.regex-rure
which builds fine now (earlier GHC versions bundle incompatible
bytestring versions).