[quake3] Optimizations for IA32

[Ryan C. Gordon]

> In any case SMP isn't truly supported, and won't be as long as it can't 
> work with SDL.

To be clear, it's not SDL that's the problem here, it's that the Linux 
3D drivers see a loss in performance with SMP (and possibly there are GL 
  and GLX implementations that aren't thread safe). Dual CPUs will not 
help, either.

We could wedge glX code into the sdl_glimp.c to switch between contexts 
like we did for Mac OS X, but it won't help. It helps on the Mac because 
Apple went out of their way to optimize the SMP codepath specifically 
for Quake 3.

--ryan.