Let non-x86_32 use the reference yuv2rgb conversion function.

The yuv2rgb_sse2 implementation is x86_32 only, so x86_64 can't take advantage of this optimized code path.

This requires the architecture defines to be working fully, so this can't be merged until it is fixed on the Windows side of things.
Merge pull request #138 from Sonicadvance1/yuv2rgb-64bit

Let non-x86_32 use the reference yuv2rgb conversion function.