Add icebreakers-llvm team

[spastorino]

We've discussed on Zulip about adding icebreakers-llvm as a team with minimal everything (no github, no website) as can be seen on the toml file, instead of doing this as a working group.

From what we've quickly seen on team repo by doing what I've done in the PR this group would end included in all@. What would be the best way to avoid that?.

/cc @nikomatsakis @pietroalbini @Mark-Simulacrum (this is also related to rust-lang/triagebot#169)

[pietroalbini]

So, the way I'd go to exclude them from all@ would be to create another state similar to wg = true. Bikeshedding is really welcome, maybe we should go with something like marker-team = true (I hate that name btw)?

You'll need to add a new field to the schema and use it to tweak how team members are collected. A validation rule to prevent wg = true with marker-team = true would also be nice. The most annoying part of this will be to expose the new state in the API. Unfortunately it's an enum at the moment and I'm pretty sure some integrations are exaustively matching it (at least the website does). You'll need to audit them to make sure they won't break, and ideally add a __NonExaustive to prevent this issue from happening in the future.

Just find a better name for marker-team = true please 😛

[spastorino]

@pietroalbini I've added some code, check it out and let me know if I'm lacking some stuff. In particular as I've commented I've added a feature flag to allow non exhaustive match for the enum we talked about but I guess that's not acceptable for this repo.

[spastorino]

So this PR is back to just adding the team, the infra work is done in #135

[pietroalbini]

It's not a marker-team.

[pietroalbini]

Integrations to update:

• Crater: Update the team repo crater#471
• Perf: Bump team repo rustc-perf#500
• GitHub teams membership: already updated
• Mailing lists: already updated
• Website: Bump the team repo www.rust-lang.org#930
• Triagebot: already updated

Note: the changes will need to be deployed before the checkboxes can be ticked.

[pietroalbini]

Fine on the technical side for me.

r? @nikomatsakis for merging the changes?