conditional dependency on ghc-byteorder?

[juhp]

IIUC ghc-byteorder is only needed for ghc < 8.4, so probably the dependency could be made conditional?

[Bodigrim]

ghc-byteorder is needed for GHC < 8.10, because GHC.ByteOrder was missing the crucial <include ghcautoconf.h> prior to base-4.14:

• https://hackage-content.haskell.org/package/base-4.13.0.0/docs/src/GHC.ByteOrder.html
• https://hackage-content.haskell.org/package/base-4.14.0.0/docs/src/GHC.ByteOrder.html