Update example for zig version 0.6.0.

[dauc]

Update casting to use @as builtin instead of calling type as a function as per https://ziglang.org/download/0.6.0/release-notes.html#Type-Coercion-Syntax Also removed a few places where casting wasn't needed as both the literal value and destination register are already 32-bits wide.

Update Makefile to make use of new CPU model awareness. https://ziglang.org/download/0.6.0/release-notes.html#Target-Details