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

[Matheus Izvekov via cfe-commits]

mizvekov wrote:

> 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:

I think we only need a subset of lldb tests for pure clang changes, and my experience is that those aren't as flaky.

> 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.

Yeah clarifying this would be helpful. In my past experience, this is not the expectation lldb maintainers have. I have had clang patches reverted only because they broke lldb tests on pure diagnostics / type printing improvements.

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