Make use of the $(GhcWithRegisterised) build flag from config.mk.  You
can now get an unregisterised build by *either*

	- setting GhcWithRegisterised to NO in build.mk, or
	- adding 'u' to GhcLibWays.

The former will make all compilations unregisterised, whereas the
latter will require a '-unreg' flag to be passed to the compiler to
get the unregisterised build.