HEAD broken on powerpc64le Linux

Building HEAD fails with this error on powerpc64le Linux see build log:

libraries/ghc-boot/dist-boot/build/GHC/Platform/Host.hs:6:34: error:
    Not in scope: ‘ppc_64ABI’
  |
6 | hostPlatformArch   = ArchPPC_64 {ppc_64ABI = ELF_V2}
  |                                  ^^^^^^^^^
make[1]: *** [libraries/ghc-boot/ghc.mk:3: libraries/ghc-boot/dist-boot/build/GHC/Platform/Host.o] Error 1

I suspect it will also fail on Powerpc64 (big-endian) Linux.

This is a regression.