Add x86-64-v3 baseline support

[immolo]

Adds x86-64-v3 baseline support with and without LTO to Catalyst. While not useful to Gentoo right now it will likely become something we add in the future seeings as we already have binhost support for it, so will save someone having to do the work again when that time comes.

[akhuettel]

I'd honestly prefer to do stuff like this in the specs. The subarches are better for non-binary-compatible distinctions (as, e.g., LP64 versus LP64D ABI on riscv)

[immolo]

That's fine, I just followed how we do it for x86 thinking that would be the preferred way.

Would you like a PR of the specs when I get around to switching my builds for work?