powerpc64le-unknown-linux is missing from llvm-targets

T5681 fails with:

Compile failed (exit code 1) errors were:
ghc-stage2: panic! (the 'impossible' happened)
  (GHC version 8.5.20180531 for powerpc64le-unknown-linux):
        Failed to lookup the datalayout for powerpc64le-unknown-linux; available targets: ["i386-unknown-windows","i686-unknown-windows","x86_64-unknown-windows","arm-unknown-linux-gnueabihf","armv6-unkno
wn-linux-gnueabihf","armv6l-unknown-linux-gnueabihf","armv7-unknown-linux-gnueabihf","armv7a-unknown-linux-gnueabi","armv7l-unknown-linux-gnueabihf","aarch64-unknown-linux-gnu","aarch64-unknown-linux","i3
86-unknown-linux-gnu","i386-unknown-linux","x86_64-unknown-linux-gnu","x86_64-unknown-linux","armv7-unknown-linux-androideabi","aarch64-unknown-linux-android","arm-unknown-nto-qnx-eabi","i386-apple-darwin
","x86_64-apple-darwin","armv7-apple-ios","aarch64-apple-ios","i386-apple-ios","x86_64-apple-ios"]
CallStack (from HasCallStack):
  error, called at compiler/llvmGen/LlvmCodeGen.hs:96:24 in ghc:LlvmCodeGen

Please report this as a GHC bug:  http://www.haskell.org/ghc/reportabug