switch to multilib, drop of i686

After bumping the toolchain to gcc6 we had some trouble building some of the larger packages for i686. Since every dev is using x86_64 and the number of users still on i686 arch seems quite low, the decision to drop i686 completely was made. This raised the need to switch the lib32-extra packages - used mainly by steam and wine - that where build by stripping the i686 packages in the past, to a different buildsystem. crazy was so kind to establish a full multilib toolchain for that and some scheme (cross32.sh) so providing two flavors (x86_64 and lib32-extra) for one package. This work was merged yesterday and the two mentioned packages still work. If you find any issues feel free to raise some bug in the bugtracker.