steam: fix steam on x86_64

Currently steam will do a 32bit only install. On 64bit systems it won't run correctly or at least most games won't. The problem is that games supporting 64bit will run their 64bit binary because the system propagates it. But the current chroot steam env just has 32bit libs installed and the game will therefore crash.

This patch will alter buildFHSChrootEnv to support multi lib installs. For this purpose I have added new config variables to buildFHSChrootEnv--if these keep untouched the env will build as before. This means that the patch should not break any other packages utilizing buildFHSChrootEnv.

On the steam side I have added many missing libraries and made it compatible with the new system.

All games that I have tested yet worked right out of the box what just wasn't possible before.

Since steam uses ldd to find out which libraries are still missing, this patch will only work after PR #2354 has been merged.

Further I haven't tested this on a 32bit only system. So please only merge after someone got this tested.