System is Archlinux x64. I do have the 32-bit deps installed and the steam runtime is on.

[vash@vashhtpc share]$ steam
Running Steam on arch  64-bit
STEAM_RUNTIME is enabled automatically
Installing breakpad exception handler for appid(steam)/version(1405474565_client)
Installing breakpad exception handler for appid(steam)/version(1405474565_client)
/home/buildbot/buildslave_steam/steam_rel_client_ubuntu12_linux/build/src/tier0/threadtools.cpp (2024) : Assertion Failed: File exists
Assert( Assertion Failed: File exists ):/home/buildbot/buildslave_steam/steam_rel_client_ubuntu12_linux/build/src/tier0/threadtools.cpp:2024

Installing breakpad exception handler for appid(steam)/version(1405474565_client)
Uploading dump (out-of-process) [proxy '']
/tmp/dumps/assert_20140807115006_4.dmp
[2014-08-07 11:50:05] Startup - updater built Jul 15 2014 18:14:26
[2014-08-07 11:50:05] Verifying installation...
[2014-08-07 11:50:06] Verification complete
[2014-08-07 11:50:06] Shutdown
Finished uploading minidump (out-of-process): success = yes
response: CrashID=bp-9a0ff7f9-af22-4376-b84f-1d9da2140807

Let me know if any specific specs would be helpful. I'll upload the dump also if helpful, I figured the CrashID probably gives it to you anyway but I backed it up anyway.