ntdll: Add SDL video driver variables to the special variables list.
Overriding the SDL_VIDEODRIVER variable (for Wayland support as an example)
on the Linux side can lead to some games under Wine failing to load (so treat
that variable as special).
ntdll: Add SDL audio driver variables to the special variables list.
This has the same issue as the video driver variable (but on a smaller
scale because games more rarely use SDL for audio).