Distinguish the architectures powerpc64 and powerpc64le?

[mpilgrem]

The common values of System.Info.arch (from base) include powerpc64 and powerpc64le. Cabal-syntax's Distribution.System.archAliases (not exported, but underpinning buildArch) maps both of those values to the single data constructor Distribution.System.PPC64 :: Distribution.System.Arch.

A user of Stack considers that the two architectures should be distinguished (see commercialhaskell/stack#6379). (Stack makes use of Cabal-syntax's Distribution.System.buildPlatform.)

I assume if they were distinguished, Cabal would map powerpc64 to the existing PPC64 and powerpc64le to a new constructor, say PPC64LE.

There would be an interaction with GHC's Hadrian:
https://gitlab.haskell.org/ghc/ghc/-/blame/master/hadrian/src/Hadrian/Haskell/Cabal.hs#L62

@bgamari, FYI.