Optimise autotools/run-in-tempdir

I made a mistake when adding support for htools to run-in-tempdir, by
needlessly copying the htools binaries, when it's enough to link
them. The copying is only really needed for python code, so we change
the Haskell binaries to linking and also a few other directories.

Difference:
- before: 0.8s, 95MB copied
- after: 0.6s, 6.2MB copied

And, by the way, can't wait for Python 2.6 as minimum supported
version…

Signed-off-by: Iustin Pop <iustin@google.com>
Reviewed-by: Guido Trotter <ultrotter@google.com>