.github: cross-compile powerpc64 Linux asset

[ee7]

Continue the recent zig cc work, such that the next configlet release will have two new release assets:

configlet_4.0.0-beta.n_linux_powerpc64.tar.gz
configlet_4.0.0-beta.n_linux_powerpc64.tar.gz.minisig

where the archive contains the executable:

$ file ./configlet
./configlet: ELF 64-bit MSB executable, 64-bit PowerPC or cisco 7500, OpenPOWER ELF V2 ABI, version 1 (SYSV), statically linked, stripped

The powerpc64-linux-musl target will have Tier 1 Zig support.

Note that powerpc64 is big endian.

Refs: #24
Closes: #810

---

To-do:

• Fix configlet lint
• Fix configlet --help
• Fix configlet completion
• Re-check configlet create|fmt|generate|info|sync|uuid|--version

[ee7]

The newly built executable doesn't pass my local testing (note #790 and #791).

When running with qemu, some configlet commands produce an error. I would guess that these errors would also occur if the executable was run natively.

I'm not surprised by the errors. It looks like some of our dependencies assume that the platform is little endian, but powerpc64 is big endian.

I'll set this PR as a draft for now.

$ qemu-ppc64-static ./configlet lint -t /path/to/exercism-tracks/nim                                                                                                                                                      
[...]

The value of `online_editor.indent_style` is `space`, but it must be one of {"space", "tab"}:
/path/to/exercism-tracks/nim/config.json

A `files.solution` value is `%{snake_slug}.nim`, which is not a valid file pattern. Allowed placeholders are: %{kebab_slug}, %{snake_slug}, %{pascal_slug}, and %{camel_slug}:
/path/to/exercism-tracks/nim/config.json
[...]

$ qemu-ppc64-static ./configlet completion -s bash
Error: Invalid buffer, unable to uncompress
supersnappy.nim(112)     uncompress
Error: unhandled exception: Invalid buffer, unable to uncompress [SnappyError]

[ErikSchierboom]

I'm not surprised by the errors. It looks like some of our dependencies assume that the platform is little endian, but powerpc64 is big endian.

Ah, the joys of endianness