Configure triagebot to accept codegen-{gcc,cranelift} ping groups and document ping groups and ping commands

[jieyouxu]

Blocked on rust-lang/team#1685.
Discussion: #t-infra > Triagebot ping groups for GCC and cranelift backends.
Closes #138116.

r? ghost

[jieyouxu]

@rustbot blocked (rust-lang/team#1685)

[jieyouxu]

I'm probably going to not add those aliases (more ways to do the same thing becomes even more confusing).

[jieyouxu]

I dropped the aliases to avoid more ways to do the same thing to avoid it getting more confusing.

[RalfJung]

The name seems inconsistent with the LLVM backend ping group which is @rustbot ping llvm (not codegen-llvm).

[jieyouxu]

@RalfJung you also fell for the classic "llvm" ping group trap 😆

It is not. llvm is an alias for llvm icebreakers ping group, see

https://github.com/rust-lang/rust/blob/master/triagebot.toml#L48-L49

this was brought up in wg-llvm zulip thread before since I've made this same mistake of thinking llvm pings wg-llvm (that we should retire the icebreakers ping group and redirect llvm to ping wg-llvm)

-- #138120 (comment)

[RalfJung]

https://rustc-dev-guide.rust-lang.org/notification-groups/llvm.html doesn't say it has anything to do with icebreakers. Was the meaning of that name changed at some point?

[jieyouxu]

Possibly, but that might've been a while ago