The official page says: SDL [nb: SDL2] officially supports Windows, Mac OS X, Linux, iOS, and Android. Support for other platforms may be found in the source code.
I would add [Raspberry Pi](http://www.raspberrypi.org/forums/viewtopic.php?t=58180&p=469283), just not maemo (nemo has SDL2). I think loongson is mips, debian on mips does have sdl2.

I had forgotten about Qt, I had to skim again to get the relationship but Qt works without SDL and optionally uses it for joystick support. I think using Qt on those platforms works, I was just hoping for SDL2 to be the better "portable platform".