After some recent changes BLI_math_base got (indirectly) included
from DNA file, causing defines conflict in Cycles: Cycles wants the
default fast behavior of square root, and BLI color wants it to be
more preciese.
Proposed solution is to move the SSE block away from the math_base
closer to code which uses it. The initial intent was to make those
functions reusable, but for a long long time the color utilities
are the only users of those functions.
This change does not prevent the error from re-occurring in the
future if some code includes sse2neon and BLI color utilities, but
it makes such conflict situation much less likely to happen, for
now.
The downside of this change is that the code now need to include
BLI_simd.h explicitly to access BLI_HAVE_SSE2 instead of relying
on it being included indirectly with math headers. The mitigation
for this is to change semantic of the BLI_HAVE_SSE2: now it is
defined to 1 if SSE2 is supported and to 0 otherwise. This makes
it so the code needs to check if using `#if BLI_HAVE_SSE2` and
if the BLI_simd.h is not included it will generate warning when
using GCC or Clang.
This change in semantic is is something the current patches would
need to ensure is handled correctly.
Pull Request: https://projects.blender.org/blender/blender/pulls/109664
5907ab0364