Blender Git Loki

Build deps: Enable SSE optimization for FFmpeg

The description is self-explanatory: enable SSE optimizations in the
FFmpeg library. They were disabled from the very beginning of the
dependency builder, possibly due to portability concerns.

FFmpeg does perform runtime check for available CPU microarchitectures,
so the codecs will still run on older hardware, but they will run way
faster on newer hardware.

For example, re-encoding 3405 2560x1376 frames on Xeon E5-2699 V4 CPU
went down from 313sec to 210.

Differential Revision: https://developer.blender.org/D8594