quirks: Fixes for symbol-based quirks to force X11

[sulix]

Make some changes to how the automatic quirks for apps which link against gl[x]ew and Cg functions work. In particular:

• They can be overridden by a user-set SDL_VIDEODRIVER env variable.
• They only print warnings if debug logging (SDL12COMPAT_DEBUG_LOGGING=1) is enabled, to match the other quirks.
• No message is printed if the user set SDL_VIDEODRIVER=x11 manually anyway.
• The messages are no-longer wrapped.

Fixes: 2a96bb35d756 ("quirks: Force X11 on Linux if certain symbols are in the process.")

In short, it now behaves more like the other quirks.

Note that there are some downsides to this:

• The messages are probably useful enough, even to people who don't typically enable debug logging.
• A number of setups will set SDL_VIDEODRIVER by default, so it won't be overridden. (And, without debug logging, will fail silently, as before.)
• Those messages are quite long, so wrapping is not without its merits.

On the whole, though, I think this is worthwhile. I've definitely managed to get several Cg games working under wayland using a hacky LD_PRELOADed shim, which requires some way of overriding the quirk here.

[icculus]

I wonder how hard it would be to bind a socket, force DISPLAY to point at it, and speak just enough of the X11 protocol to make these apps survive extension lookup and glXGetProcAddress. :)

[icculus]

(for future reference: GitHub's "here's how to update this PR from the command line" instructions don't update the PR, they push right to main. :/ )