This commit updates all defines, compiler flags and cleans up some code for unused CPU capabilities.
There should be no functional change, unless it's run on a CPU that supports sse41 but not sse42. It will fallback to the SSE2 kernel in this case.
In preparation for the new SSE4.2 minimum in Blender 4.2.
Pull Request: https://projects.blender.org/blender/blender/pulls/118043
While keeping SSE2, SSE4.1 and AVX2. This does not affect hardware support, it
only slightly reduces performance for some older CPUs.
To reduce maintenance cost and improve compile times.
Differential Revision: https://developer.blender.org/D16978
* Replace license text in headers with SPDX identifiers.
* Remove specific license info from outdated readme.txt, instead leave details
to the source files.
* Add list of SPDX license identifiers used, and corresponding license texts.
* Update copyright dates while we're at it.
Ref D14069, T95597
Remove prefix of filenames that is the same as the folder name. This used
to help when #includes were using individual files, but now they are always
relative to the cycles root directory and so the prefixes are redundant.
For patches and branches, git merge and rebase should be able to detect the
renames and move over code to the right file.
