Drop Support for Unused/Abandoned Architectures

[insertinterestingnamehere]

We currently have a ton of old untested ifdefs for a bunch of crazy architectures that don't really exist in practice anymore (e.g. Tilera). We should get rid of that code.

Architectures I think we should definitely get rid of:

• IA64
• Alpha
• MIPS
• Power PC 32-bit
• Sparc
• TILEPro
• TILE-Gx

Others that I'd like to get rid of too:

• 32-bit x86 (In our code as IA32)
• 32-bit ARM and
• ARM v7 (not in our code as distinct from 32-bit ARM)

[insertinterestingnamehere]

Alright, from internal discussion it sounds like we're just supporting x86-64, ARM64, and maybe power9 going forward, so the next thing to do here is purge all the ifdefs and build configuration cruft for everything else. Once that's done I think this issue is good to close.

[insertinterestingnamehere]

I'm including the PR dropping Tilera, Itanium, MIPS, and Sparc architectures in the 1.21 release. I'm clearing this issue from the release milestone though since the 32-bit stuff is still there.

[insertinterestingnamehere]

Fixed in #273.