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

[Michael Buch via cfe-commits]

Michael137 wrote:

> Given the libc++ experience, let's move forward with this PR as-is. If there's an issue in practice, we'll disable the tests on changes to Clang at that point.

Do note that libc++ CI only runs a subset of the LLDB tests. Only the ones that are impacted by libc++. We could take the same approach for clang if we find the whole test-suite to be too flakey i suppose

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