Long ago, UI tests were divided into "compile" and "run" tests. Later, the
compile tests were further subdivided into "check" and "build" tests, to speed
up tests that don't need a full build.
The same split was never applied to incremental test revisions, so the only way
to perform a check build in incremental tests is (confusingly) to use a `cfail`
revision and then specify `//@ check-fail` or `//@ check-pass`.
This PR makes room for dedicated check-fail and check-pass revisions by
renaming the existing `cfail` and `cpass` revisions to `bfail` and `bpass`,
since they currently perform a full build.
This currently works because it's part of expansion, and that isn't yet
tracked by the query system. But we want to ensure it continues working,
even if that is changed.
Zalathar