It appears that previously, assembly was straight up disabled for all ARM64 platforms in x264 - this re-enables it.
This also updates the version of FFmpeg to 7.1.1. I updated the patch files so that they would cleanly apply to 7.1.1.
For Windows ARM64, it also switches both of these libraries to use the copy of LLVM we build as part of the deps, instead of MSVC - this gives a small performance increase. To do this for x264, I added a small patch taken from VCPKG - this should be harmless to other platforms.
With all these changes, I was able to get a ~20-30% perf improvement in video transcoding in the sequence editor.
Pull Request: https://projects.blender.org/blender/blender/pulls/137670
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