[llvm] [bazel] Add support for multiple tblgen outputs (PR #168158)

[Keith Smiley via llvm-commits]

keith wrote:

now https://github.com/llvm/llvm-project/pull/168355 instead but yes hopefully. i imagine something else broke on the bazel side in between, but likely just easy import changes vs something more complex like this. i will land it as soon as that one is in and then fix forward anything else

https://github.com/llvm/llvm-project/pull/168158