Cabal/Stack does not distinguish powerpc64 and powerpc64le architectures

I am building Unison for Fedora ([here](https://copr.fedorainfracloud.org/coprs/petersen/unison/)) using stack.
Today seems the first time I used stack on ppc64le without setup of ghc.

So it fails for me with
```
+ stack --system-ghc install
:
I don't know how to install GHC for (Linux,PPC64), please install manually
```
Full [build.log](https://download.copr.fedorainfracloud.org/results/petersen/unison/fedora-rawhide-ppc64le/06759906-unison/builder-live.log.gz) from https://copr.fedorainfracloud.org/coprs/petersen/unison/build/6759906/

Naively it feels like Stack.Setup is trying too hard here...
Well I have a workaround using my `stack-symlink-distro-ghc` script.
However I would like to add PPC64 and S390X Linux in the Setup module,
I am guessing they should map to `linux-ppc64` and `linux-s390x`.

Though in this case I already told stack to use the system ghc..