In the past we needed the construct below for wired-in packages,
but since GHC 8.0 (which we require at least for stage0 now) the CLI has
stabilised, so we can unconditionally use `-this-unit-id` since GHC 8.0.

    if impl( ghc >= 7.11 )
	ghc-options:  -this-unit-id template-haskell
    else
	if impl( ghc >= 7.9 )
	    ghc-options:  -this-package-key template-haskell
	else
	    ghc-options:  -package-name template-haskell