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

This adds build configuration for building LLDB on macOS and Linux. It
uses a default subset of features that should work out of the box with
macOS + Ubuntu. It is notably missing python support right now, although
some of the scaffolding is there, because of the complexity of linking a
python dylib, especially if you plan to distribute the resulting
liblldb.so.

Most of this build file is pretty simple, one of the unfortunate
patterns I had to use was to split the header and sources cc_library
targets to break circular dependencies.