Tracking issue for changes to target triples

[madsmtm]

Since #1413, cc parses the rustc target when running outside build scripts. To ensure that this is kept up-to-date with changes to rustc, there's a CI step that runs every so often, and adds a comment here if the latest nightly failed.

Resolving this requires a code change (which is why we don't open a PR to do it automatically). Resolved comments will be hidden.