Blender Git Loki

Fix T53068: AMD Threadripper not working well with Blender

The issue was caused by SpinLock implementation in old pthreads we ar eusing on
Windows. Using newer one (2.10-rc) demonstrates same exact behavior. But likely
using own atomics and memory barrier based implementation solves the issue.

A bit annoying that we need to change such a core part of Blender just to make
specific CPU happy, but it's better to have artists happy on all computers.

There is no expected downsides of this change, but it is so called "works for
me" category. Let's see how it all goes.