steam: libstdc++/mesa incompatibility workaround

closes #9003

pkgs/games/steam/chrootenv.nix

···
 
   profile = ''
     # Ugly workaround for https://github.com/ValveSoftware/steam-for-linux/issues/3504
-    export LD_PRELOAD=/lib32/libpulse.so:/lib64/libpulse.so:/lib32/libasound.so:/lib64/libasound.so
+    export LD_PRELOAD=/lib32/libpulse.so:/lib64/libpulse.so:/lib32/libasound.so:/lib64/libasound.so:$LD_PRELOAD
+    # Another one for https://github.com/ValveSoftware/steam-for-linux/issues/3801
+    export LD_PRELOAD=/lib32/libstdc++.so:/lib64/libstdc++.so:$LD_PRELOAD
   '';
 
   runScript = "steam";