Fallback code paths with "SIMD Everywhere"

https://github.com/simd-everywhere/simde has done their first release ( https://simd-everywhere.github.io/blog/announcements/release/2020/06/21/0.5.0-release.html ) and it seems like something potentially useful for merging code paths. The most likely candidate I imagine is using SIMD code to replace the non-SIMD fallback path, but maybe it'd be worth checking if it can be used to merge ARM and x86_64 or support other architectures