Blender Git Loki

Cycles: use safe compiler flags for OpenCL.

Using -cl-fast-relaxed-math assumes no NaN/Inf values in any expression.
This causes problems on overflow, division by zero, square root of negative number.
Comparisons with NaN or infinite value are affected as well.

This patch causes <2% slowdown on benchmark scenes.

Fix T50985: Rendering volume scatter with GPU OpenCL comes to an halt after a few seconds