Blender Git Loki

Cycles: Implement threaded SVM nodes compilation

The title says it all actually. From tests with barber shop scene here
gives 2-3x speedup for shader compilation on my oldie i7 machine. The
gain is mainly due to textures metadata query from jpeg files (which
seems to requite de-compression before metadata can be read). But in
theory could give nice improvements for scenes with huge node trees
as well (i'm talking about node trees of complexity of fractal which
we had reports about in the past).

Reviewers: juicyfruit, dingto, lukasstockner97, brecht

Reviewed By: brecht

Subscribers: monio, Blendify

Differential Revision: https://developer.blender.org/D2215