Build the sdl package via sdl12-compat instead of SDL 1.2

SDL 1.2 does not receive much attention any more, and upstream does not recommend using it[1]. There is, however, the replacement called sdl12-compat which implements the SDL 1.2 API and ABI using SDL 2.0, which means you gain things such as Wayland support, better support for various input devices, and native PipeWire audio support. Fedora is making this change as of Fedora 35 (the next release)[2] and has a nice write-up about this change, linked below.

This also solves an issue in postmarketOS where we want to set SDL_VIDEODRIVER=wayland globally for Wayland UIs as SDL(2) works significantly better in native Wayland mode on phones, but doing this currently breaks SDL 1.2 applications as those then cannot find any video driver with this set:

[neboula@nocturne ~]$ SDL_VIDEODRIVER=wayland icebreaker 
Hey. We're gonna need some graphics.
SDL error: No available video device

This should not be an issue with sdl12-compat as it uses SDL 2 behind the scenes, so this should be handled the same way in both.

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