[llvm] [bazel] Add support for building lldb (PR #87589)

[Jordan Rupprecht via llvm-commits]

rupprecht wrote:

I landed bee33770188f29d0369655c6d178c0bfb937e872 to make buildkite green.

As for why we do query+test instead of just test: I think this comes from https://github.com/openxla/iree/blob/bb7e536ecd31ea24007aa7202f3a0c41b897e05c/build_tools/bazel/build_test_all.sh

```
# We use `bazel query //...` piped to `bazel test` rather than the simpler
# `bazel test //...` because the latter excludes targets tagged "manual". The
# "manual" tag allows targets to be excluded from human wildcard builds, but we
# want them built by CI unless they are excluded with tags.
```

While that may be true for iree, I don't think it's (currently) true for LLVM. i.e., I don't know if we have any `tags = ["manual"]` stuff that we explicitly want to build in CI.

---

Separate from the buildkite issue: we have some internal rules for building LLDB, and they look a bit different than this, but that's partly because it requires a bunch of other internal stuff. I'll see if there's anything we have that we can contribute.

https://github.com/llvm/llvm-project/pull/87589