bannerlator-steam-x64: the SteamRT platform libraries after the rootfs's

steamui.so needs GTK 2 (libgtk-x11-2.0.so.0), which the SteamRT container
provides and FEX's Ubuntu 24.04 rootfs does not. Append Valve's own
steamrt3c platform library directories to the client's library path,
after the rootfs.

tools/linuxfs/overlay/usr/local/bin/bannerlator-steam-x64

@@ -166,6 +166,12 @@ exit 0
   export STEAM_RUNTIME_STEAMRT=$srt_shim
 fi
 export LD_LIBRARY_PATH=$STEAM_X64/steamrt64:$STEAM_X64/steamrt64/panorama
+# The libraries the SteamRT container would give the client and the rootfs lacks (GTK 2 for
+# steamui.so, ...): Valve's own platform runtime files, last, so the rootfs's copies come first.
+for d in "$STEAM_X64"/steamrt64/pv-runtime/steam-runtime-steamrt/steamrt3c_platform_*/files/lib/x86_64-linux-gnu \
+         "$STEAM_X64"/steamrt64/pv-runtime/steam-runtime-steamrt/steamrt3c_platform_*/files/usr/lib/x86_64-linux-gnu; do
+  [ -d "$d" ] && LD_LIBRARY_PATH=$LD_LIBRARY_PATH:$d
+done
 # After an update the client re-executes itself inside the SteamRT container through
 # pressure-vessel-wrap, which needs bwrap. The FEX rootfs with the client's own steamrt64 libraries
 # is that container here; the client's recursion guard says it is already inside one.