This should fix issues where -32bit packages are missing the runtime
dependencies, since the common/hooks/post-install/98-shlib-provides.sh
hook depends on the 32bit files being copied and the runtime and the
rdep part of the common/hooks/post-install/80-prepare-32bit.sh depends
on the common/hooks/post-install/98-shlib-provides.sh.
In a later change, we will generate shlib-depends cross subpkgs during
pre-pkg stage. Thus we need shlib-provides information of all subpkgs
ready before pre-pkg is run.
Those information can only be read in post-install stage at the
eariliest.
Let's move the shlib-provides to post-install. This hook requires
prepare-32bit, so, let's move that hook, too.