Commit 0055c6a introduced a new preConfigure hook that sets the right
qmake path. Unfortunately the mkDerivation attributes of qgroundcontrol
override the whole configurePhase, so this hook isn't run at all.
Instead of using pushd/popd, I'm making it a bit more readable by just
spawning a subshell with the right working directory.
This fixes the build of qgroundcontrol and it now successfully compiles
on my machine.
Signed-off-by: aszlig <aszlig@redmoonstudios.org>
11294eaf16