Graphics drivers not all captured

To reproduce:

• overwrite SteamLinuxRuntime_soldier/pressure-vessel/ with one built from 3a8f6c28
• launch Portal 2 (with PRESSURE_VESSEL_SHELL=instead)
• steam-runtime-system-info
• "$@"
• "$@" -vulkan

Expected result: gfx drivers work

Actual result: not all dependencies of gfx drivers are available and they fail to load

I'm looking into it. I blame the optimizations that I did on the way to !433 (merged).