32-bit support

[woodruffw]

KRF currently makes x86 specific assumptions, and may make x86_64-specific assumptions. We should try to eliminate the latter (if they exist) so that it can be built with support for x86_32-specific syscalls (e.g., iopl(2) in #6).

This has two parts:

• Investigating the general feasibility of x86_32 bit builds + ensuring that KRF actually works when built in 32-bit
• Refactoring the codegen/specs to only generate syscalls for the relevant platform (e.g., not emitting iopl(2) on x86_64)