I don't know if this is the correct place to report a problem with Steam games,
but the problem is unique to Tumbleweed.  If I should report this elsewhere,
please do say, and I will.

The gist of it is that Portal and Civilization 5 segfault upon starting the
game.  I tracked this down to the following Arch bug report:

https://bugs.archlinux.org/task/54136

The Arch people fixed this by compiling libc with -mstackrealign.  I don't
truthfully know whether that is a viable solution for the openSUSE project.

The backtrace for Civilization 5 is as follows:

(gdb) bt
#0  0xf7a2e7c3 in __strspn_sse42 () from /lib/libc.so.6
#1  0xef78f5a6 in pa_config_parse () from
/usr/lib/pulseaudio/libpulsecommon-10.0.so
#2  0xef780e9b in pa_client_conf_load () from
/usr/lib/pulseaudio/libpulsecommon-10.0.so
#3  0xefb82264 in pa_context_new_with_proplist () from /usr/lib/libpulse.so.0
#4  0xefb823ce in pa_context_new () from /usr/lib/libpulse.so.0
#5  0xf780a78a in ?? () from /usr/lib/libopenal.so.1
#6  0xf780c3e7 in ?? () from /usr/lib/libopenal.so.1
#7  0xf77d8553 in ?? () from /usr/lib/libopenal.so.1
#8  0xf7b897e5 in __pthread_once_slow () from /lib/libpthread.so.0
#9  0xf77d9985 in alcOpenDevice () from /usr/lib/libopenal.so.1
#10 0x09126f34 in YUV12 ()
#11 0x091264a2 in YUV12 ()
#12 0x09113bee in check_for_pending_io ()
#13 0x09114188 in BinkOpen ()
#14 0x085f7553 in ASL::PlayBinkMovieGL(char const*, float, unsigned int,
unsigned int, bool*) ()
#15 0x0884c26c in PlayMovieState::Begin() ()
#16 0x086e0fc3 in Civ5App::PlayOpeningMovie() ()
#17 0x086e1c46 in Civ5App::Init(char const*) ()
#18 0x0865b3ed in WinMain ()
#19 0x085f5487 in ?? ()
#20 0x085d8e3e in ThreadHANDLE::ThreadProc(void*) ()
#21 0xf7b81328 in start_thread () from /lib/libpthread.so.0
#22 0xf79d3606 in clone () from /lib/libc.so.6

The backtrace for Portal is similar, but I don't have it at hand at the moment.
 I will add it soon.