[compiletest] support `known-bug` directive for more test suites

currently, it is only supported for ui tests, but it would be nice to also have it for at least the following:
* [ ] `rustdoc`
* [ ] `rustdoc-js`
* [ ] `run-make`
* [ ] `rustdoc-json`

documentation for how `known-bug` works is sparse, so it's not entirely clear how it would interact with other test suites.