[cvs-nhc98] Fix error (nthcon: n==0 con==37) due to an interface file

[Malcolm Wallace]

> I also had to compile src/prelude/Hat/Hat.hs by hand with "+RTS -K2M":
>   ...
> (I couldn't find an environment variable for default options to NHC
> easily - is there one?)

If `hmake' is being used, then HFLAGS is the variable to use, but
otherwise there is no environment variable for default options in
nhc98, no.

For building the prelude and libraries, we usually add a
couple of lines to the appropriate Makefile, in this case
src/prelude/Hat/Makefile, something like

    ifeq "${BUILDWITH}" "ghc"
    HEAP = +RTS -K2M -RTS
    endif

    EXTRA_H_FLAGS   = $(HEAP)

Regards,
    Malcolm