https://bugs.freedesktop.org/show_bug.cgi?id=76082
--- Comment #7 from Laurent carlier lordheavym@gmail.com --- (In reply to comment #6)
And steam probably uses LD_LIBRARY_PATH. According to http://blog.tremily.us/posts/rpath/, the rpath actually comes first. So my change should probably be reverted, since it disallows using LD_LIBRARY_PATH.
Can you see if starting steam with STEAM_RUNTIME=0 fixes things for you?
Sorry i wasn't able to run Metro LL with STEAM_RUNTIME=0, even with mesa without your patch