cmst: Fix running of {pre,post}Configure

Commit 0055c6aa

 introduced a new preConfigure hook that sets the right
qmake path. Unfortunately the mkDerivation attributes of cmst override
the whole configurePhase, so this hook isn't run at all.

I've also added running the preBuild and postBuild hooks for the sake of
completeness so that it's easier to override the derivation attributes.

This fixes the build of cmst and it now successfully compiles on my
machine.

Signed-off-by: aszlig <aszlig@redmoonstudios.org>