Support NEON (aarch64)

[dievsky]

With Apple M1 gaining popularity, it makes sense to support its SIMD capabilities (NEON).
Unfortunately, boost.simd doesn't support NEON, so we have to either modify boost.simd to add said support, or somehow use NEON directly.

[dievsky]

Anyone willing to contribute could investigate how we can add NEON support to our fork of boost.simd. After that, adding another assembly target to viktor itself should be easy enough.

[dievsky]

boost/simd/arch contains definitions for various architectures that seem to bridge the native SIMD types and the boost::simd vectors. We need such a bridge for aarch64/neon.

[torb-no]

Has there been any progress on this?
Also, what would happen if you did use Viktor on ARM Macs? Would it degrade gracefully or outright fail?

[olegs]

@torb-no Unfortunately, no progress so far. However, any help or even a pull request is appreciated!