[llvm] [Bazel] Support opt-driver library, like clang-driver (PR #79205)

[Eli Friedman via llvm-commits]

https://github.com/efriedma-quic requested changes to this pull request.

If we're going to make opt-driver a library, it should be a library for both CMake and Bazel builds.  The set of available libraries shouldn't depend on how you build LLVM.

https://github.com/llvm/llvm-project/pull/79205