Arch Linux

Description:
For a while now, bundled libstdc++.so.6 is not compatible with the current open source Radeon driver.
However using

LD_PRELOAD=/usr/lib32/libstdc++.so.6 steam

throws other errors (ERROR: ld.so: object '/usr/lib32/libstdc++.so.6' from LD_PRELOAD cannot be preloaded (wrong ELF class: ELFCLASS32): ignored.) but steam is started then. I'd rather have the right version packed with it, if this doesn't break anything else in the packet.

Additional info:
Package version(s):
multilib/steam 1.0.0.52-2
extra/mesa 11.2.1-1
extra/mesa-libgl 11.2.1-1
multilib/lib32-mesa 11.2.1-1
multilib/lib32-mesa-libgl 11.2.1-1
core/linux 4.5.2-1

CPU: AMD A10-7850K Radeon R7, 12 Compute Cores 4C+8G

Graphics Card (integrated R7)
00:01.0 VGA compatible controller: Advanced Micro Devices, Inc. [AMD/ATI] Kaveri [Radeon R7 Graphics]
Subsystem: ASUSTeK Computer Inc. Device 85cb
Kernel driver in use: radeon
Kernel modules: radeon

Log:
michael@arch ~ % LIBGL_DEBUG=verbose steam
Running Steam on arch rolling 64-bit
STEAM_RUNTIME is enabled automatically
Installing breakpad exception handler for appid(steam)/version(1461972496)
libGL: OpenDriver: trying /usr/lib32/xorg/modules/dri/tls/radeonsi_dri.so
libGL: OpenDriver: trying /usr/lib32/xorg/modules/dri/radeonsi_dri.so
libGL: dlopen /usr/lib32/xorg/modules/dri/radeonsi_dri.so failed (/home/michael/.local/share/Steam/ubuntu12_32/steam-runtime/i386/usr/lib/i386-linux-gnu/libstdc++.so.6: version `GLIBCXX_3.4.21' not found (required by /usr/lib32/xorg/modules/dri/radeonsi_dri.so))
libGL error: unable to load driver: radeonsi_dri.so
libGL error: driver pointer missing
libGL error: failed to load driver: radeonsi
libGL: OpenDriver: trying /usr/lib32/xorg/modules/dri/tls/swrast_dri.so
libGL: OpenDriver: trying /usr/lib32/xorg/modules/dri/swrast_dri.so
libGL: dlopen /usr/lib32/xorg/modules/dri/swrast_dri.so failed (/home/michael/.local/share/Steam/ubuntu12_32/steam-runtime/i386/usr/lib/i386-linux-gnu/libstdc++.so.6: version `GLIBCXX_3.4.21' not found (required by /usr/lib32/xorg/modules/dri/swrast_dri.so))
libGL error: unable to load driver: swrast_dri.so
libGL error: failed to load driver: swrast

Steps to reproduce:
With appropriate hardware & system install steam through pacman and run it with

LIBGL_DEBUG=verbose steam