Add FreeBSD support

[purefns]

This issue is meant to track progress on adding support for FreeBSD systems for the following items:

• Compile/run the builder via zig build
• Compile/run all examples via zig build -Dexample=[NAME]
  • Finish all examples for each chapter #18
• All example binary/test runs work as expected
  • Finish all examples for each chapter #18
  • Skip running aarch64 binary for cross-compilation example entirely #11

[purefns]

This is currently blocked by the same example that is blocking Windows support: cross-compilation.

Zig cannot cross-compile for aarch64-freebsd on x86_64-freebsd breaking this example entirely.

Otherwise, we need to use zig libc and the --libc <path> flag to pass include/lib directories to lld when running zig build-exe.

[purefns]

Everything is running very well on FreeBSD right now. The self-hosted runner I spun up for the Zig tests is working flawlessly 😄