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.
Zalathar