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

[Pranav Kant via llvm-commits]

pranavk wrote:

@keith we are very interested in getting this merged. 

Just to make sure we are on same page. After #168409, this PR should be able to fix the broken bazelbot. No other pending issues, right?

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