on when to build ghci libs in cabal

[Isaac Jones]

Henning Günther and Duncan Coutts / the Gentoo team have sent me a
patch to move creation of ghci libs to the build phase rather than the
register phase.  It makes more sense there and should be somewhat
better for debian and gentoo.

Though Duncan points out that maybe some ppl want to build the ghci
libs during register because it could save room in a binary
distribution (like debian and rpm).  Any opinions here?

Also, I noticed the "FIXME" that mentions the -x flag is only
supported on some platforms; what effect will this have on platforms
that don't support it?  Will they be broken during build?  What about
platforms where we know the ghci libs don't work, like MacOS; will
this patch cause building to break?

The patch adds a couple extra configure options,
--enable-library-for-ghci / --disable-library-for-ghci.  I'm sorta
thinking of just having one option "--disable-interpreter-libs" or
something to make this seem more generic, though at the moment, it
still only makes sense for a combo compiler / interpreter build (that
is, --ghc).  I'll be happy to add this to the manual once we settle on
a flag.  Do we ever really need to disable it anyway?

peace,

  isaac