xbps-src: run pre-pkg hooks in the install to destdir target.

The prepare-32bit hook has been moved to the pre-pkg stage and now
those hooks are executed as part of the install phase. That means that
pre-pkg hooks are now independently run for the subpkgs and the sourcepkg
after the install-destdir phase and pre/do/install hooks.

As bonus, finally correct rdeps can now be collected for the 32bit pkgs
and works for all them, without the need to sort the order of subpkgs!