sdist should not have to build everything
It would be nice if instead of
$ perl boot $ ./configure $ make $ make sdist
it would suffice to run
$ perl boot $ ./configure $ make sdist
and if that would not build more than necessary to generate the tarballs.
It would save time on the GHC-HEAD-Debian-Package-autobuilder that I am currently working on.
I might look into this bug eventually, but if someone else feels like doing it: Even better. (Difficulty estimated conservatively; might well be less than an hour, besides maybe waiting for test runs to finish :-))
Remember to update MakingReleases and Building/StandardTargets if this is implemented.