Commit 0055c6a introduced a new preConfigure hook that sets the right
qmake path. Unfortunately the mkDerivation attributes of qwt override
the whole configurePhase, so this hook isn't run at all.
This fixes the build of qwt and it now successfully compiles on my
machine.
Signed-off-by: aszlig <aszlig@redmoonstudios.org>
8779e0f274