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>
'qgis', one of the few 'qwt' dependees in nixpkgs, fails to build with
qwt 6. So I'm not moving the default version away from 5.x. Also, not
changing the default allows easy/safe cherry-picking to the stable
branch.