Blender Git Loki

Fix T78047: Fix failing denoiser tests on windows

When we switched to MSVC2019 and C++17 we seemingly
managed to trigger a code-gen bug with MSVC in the
AVX code-path.

This change works around the issue by (hopefully
temporary) disabling the optimizer for the fast_exp2f4
function, given it is only used in a single pass
of the denoiser and nowhere else, this is luckily
not as bad as it could have been.

Once the compiler is fixed or a different fix is
available we'll have to revisit this.

Details and link to the repro posted to MS is
available in T78047