Log driver-selection environment variables
Some drivers have an environment variable that overrides the automatic
detection of which driver should be used. For example Mesa has
MESA_LOADER_DRIVER_OVERRIDE
, VA-API has LIBVA_DRIVER_NAME
and so on.
We now log these environment variables in the s-r-s-i output to have a move complete view about the state of the running system.
/cc @smcv @jpwhiting