[clang] [llvm] Enable LLDB tests in pre-merge CI (PR #94208)

[Aaron Ballman via cfe-commits]

https://github.com/AaronBallman commented:

I think it makes a lot of sense for lldb to have a precommit CI pipeline which tests changes to lldb. I don't think we're at a point where it would make sense to enable lldb precommit CI testing for changes to clang, though.

For starters, the false positive rate from flaky lldb test failures is pretty high:

https://lab.llvm.org/buildbot/#/builders/17/builds/53939
https://lab.llvm.org/buildbot/#/builders/68/builds/75367
https://lab.llvm.org/buildbot/#/builders/219/builds/11908
https://lab.llvm.org/buildbot/#/builders/219/builds/11819
https://lab.llvm.org/buildbot/#/builders/219/builds/11810
https://lab.llvm.org/buildbot/#/builders/96/builds/58350

But also, changes in Clang that break lldb do not necessarily mean that a PR is not ready to land. There are conforming changes that can be made to Clang which lldb needs to react to as a downstream consumer of Clang as a library rather than a PR author needing to react to it. (e.g., adding a new AST node to Clang or changing diagnostic wording/behavior). We should try to come up with and document a policy about what the expectations are regarding Clang and lldb interactions before we add lldb to Clang's precommit CI pipeline.

https://github.com/llvm/llvm-project/pull/94208