continuation of #109595
pkgconfig was aliased in 2018, however, it remained in
all-packages.nix due to its wide usage. This cleans
up the remaining references to pkgs.pkgsconfig and
moves the entry to aliases.nix.
python3Packages.pkgconfig remained unchanged because
it's the canonical name of the upstream package
on pypi.
Commit 0055c6a introduced a new preConfigure hook that sets the right
qmake path. Unfortunately the mkDerivation attributes of iannix override
the whole configurePhase, so this hook isn't run at all.
This fixes the build of iannix and it now successfully compiles on my
machine.
Signed-off-by: aszlig <aszlig@redmoonstudios.org>
