Blender Git Loki

Fix automated tests when building with GCC and march=native

When building with more aggressive optimization flags, GCC will add FMA
(Fused Multiply Add) instructions that will slightly alter the floating
point operation results.

This causes some automated tests to fail in blender.

In clang and the intel compiler ffp-contract is set to off per default
it seems from my research. (They do not have the exact same setting,
but the default seems to match the off behavior)

Reviewed By: Brecht

Differential Revision: https://developer.blender.org/D9047