Setup.hs: unbreak 'runhaskell Setup configure' building mode

Otherwise default hook won't generate src/GitRev.hs file.

Signed-off-by: Sergei Trofimovich <slyfox@gentoo.org>
Merge pull request #23 from trofi/master

Setup.hs: unbreak 'runhaskell Setup configure' building mode

Adds autoconf hooks by default; should have no effect for systems building with `make`