[llvm] [libc][bazel] Add a helper library with all deps of generated headers. (PR #136582)

[Michael Jones via llvm-commits]

https://github.com/michaelrj-google approved this pull request.

Does the `stdbit_test` currently build? If not it might be good to disable it so that local bazel testing doesn't fail.

https://github.com/llvm/llvm-project/pull/136582