Description:
Since doing a pacman -Syu last week, Steam crashes in library code with an Illegal Instruction.

I'm running testing and mesa-git on an AMD Phenom II X6 1100T.

Additional info:
The steam executable that crashes links to these guys:
/usr/lib32/libX11.so.6 is owned by lib32-libx11 1.6.5-1
/usr/lib32/librt.so.1 is owned by lib32-glibc 2.25-7
/usr/lib32/libm.so.6 is owned by lib32-glibc 2.25-7
/usr/lib32/libdl.so.2 is owned by lib32-glibc 2.25-7
/usr/lib32/libstdc++.so.6 is owned by lib32-gcc-libs 7.1.1-4
/usr/lib32/libpthread.so.0 is owned by lib32-glibc 2.25-7
/usr/lib32/libc.so.6 is owned by lib32-glibc 2.25-7
/usr/lib32/libxcb.so.1 is owned by lib32-libxcb 1.12-2
/usr/lib32/libgcc_s.so.1 is owned by lib32-gcc-libs 7.1.1-4
/usr/lib32/libXau.so.6 is owned by lib32-libxau 1.0.8-1
/usr/lib32/libXdmcp.so.6 is owned by lib32-libxdmcp 1.1.2-1

* config and/or log files etc.

Reading symbols from steam...(no debugging symbols found)...done.
(gdb) run
Starting program: /home/arf/.local/share/Steam/ubuntu12_32/steam
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/usr/lib/libthread_db.so.1".
ILocalize::AddFile() failed to load file "public/steambootstrapper_english.txt".
[2017-07-27 07:16:20] Startup - updater built Nov 23 2016 01:05:42
[2017-07-27 07:16:20] Opted in to client beta 'publicbeta' via beta file
You are in the 'publicbeta' client beta.
Installing breakpad exception handler for appid(steam)/version(1499997556)
t
Program received signal SIGILL, Illegal instruction.
std::__detail::_NFA<std::__cxx11::regex_traits<char> >::_M_insert_matcher(std::function<bool (char)>) (this=0x56a17ce4, __m=...)
at /usr/include/c++/7.1.1/bits/regex_automaton.h:271


Steps to reproduce:
Have an old AMD processor and run steam? I'm not sure...