ARM support + os-arch-variant build architecture

[rafie]

No description provided.

[lantiga]

Hi @rafie, I tested this on my system and it worked flawlessly.

I also tested an out-of-source build, in a RedisAI-build directory parallel to the RedisAI source directory. It worked without issues, the only nit is that the install-cpu directory was created inside the source directory.

This was kind of unexpected, as I expected the install directory to be outside the source dir, but in fact placing it in the RedisAI-build directory is quite confusing too, since we'd have redisai.so in RedisAI-build and another redisai.so in RedisAI-build/install-cpu.

The ideal would be to have a RedisAI-install parallel to RedisAI-build, but we can't just create directories outside the build root.

So, long story short, we should keep it in the source tree for now :-D

I'm good to merge, but maybe we want to take this opportunity to rearrange directories as we discussed on Slack?