Issues with Win32 MMX code

Hi folks.

Mozilla had some issues with the MMX optimized frag_recon functions over 
the last days, and I was able to track the problem down. The code itself 
is fine, but it unfortunately it has the tendency to cause a 
non-deterministic compiler bug.

The whole discussion is here:

  https://bugzilla.mozilla.org/show_bug.cgi?id=474937


After thinking about the problem I've suggested to remove all optimized 
frag_recon assembler functions and replace them with MMX intrinsic based 
versions. My hope is that the problem will dissapear that way because 
the new functions will be no special cases for the compiler anymore.

If we only fix/remove the function that caused the problems (that's the 
current bug-fix) we don't win much because the problem may occur a week 
or two later at another place.

Any comments?

- Nils