sdl_gfx: 64-bit support

Hi,

I disabled 'mmx' buggy support in sdl_gfx, so it compiles on 64-bit (and doesn't crash on i386 - see below).
I also removed the 'autoreconf'iguration as everything compiled fine without.

Additional note: SDL_imagefilter.c, which uses MMX is actually rarely used, and was tested VC++. The GCC ASM version crashed due to incorrect use of popa/pusha instructions (the code didn't take the stack pointer change into account). I worked for 2 weeks on a fix using GCC intrinsics at https://gitorious.org/sdlgfx/asm/, fixing i386 and adding 64-bit support. The SDL_gfx maintainer took is for the upcoming SDL2_gfx, although there's no plan for SDL_gfx right now.