Blender Git Loki

Cycles: Implement AVX2 version of triangle_intersect

This commit basically vectorizes existing code using AVX2 instructions
(without modifying algorithm itself). This gives quite nice speedups:

BMW: -8%
Classroom: -5%
Cat: -5%
Koro: +1%
Barcelona: -8%

That's on Linux machine, reported performance improvement on Windows
goes up to 20%.

Not currently sure why Koro is somewhat slower because it mainly uses
curve intersection tests, could be a time noise? Or osmething with the
cache utilization perhaps? In any case speedup in other scenes makes
me thinking that current state is acceptable for initial implementation.

This is again inspired by Maxym Dmytrychenko.