[Feature request] Tab completion for `-Wno-`, `-Werror=`, and `=0|1|2` levels in zsh completion script

[Rangi42]

contrib/zsh_compl/_rgbasm has some TODO comments related to this.

[Rangi42]

We have two attempts at fixing this so far:

1. By @vulcandth: https://pastebin.com/KQeECWFD (generated by OpenAI Codex)
2. By @aronson: https://pastebin.com/NHHehUXm (generated by Roo Code)

I expect we can synthesize one working PR out of this.

[Rangi42]

I don't want to be responsible for maintaining these completion scripts beyond their current level of complexity. I don't think implementing such detailed -W completion support would be worthwhile: few people are running nontrivial rgbasm invocations directly from shell instead of via a Makefile or script, few people are using the completion scripts at all, and the intersection of those sets might even be zero.