Blender Git Loki

Build: disable address sanitizer for Cycles optimized kernels with GCC

It's extremely slow to compile and run, so just disable it unless
WITH_CYCLES_KERNEL_ASAN is manually enabled. For Clang it's always
enabled since that appears to work ok.

This also limits the -fno-sanitize=vptr flag to the Cycles kernel, as it
was added specifically to work around an issue there.

Differential Revision: https://developer.blender.org/D5404