[llvm] [bazel] Add td_library target for OptParser.td (PR #86363)

[Jordan Rupprecht via llvm-commits]

https://github.com/rupprecht approved this pull request.

Other packages are able to refer directly to `OptParser.td` as exported by `export_files`, e.g. https://github.com/llvm/llvm-project/blob/4e6745cc4db309c0e1b5e41d4598f67763f4c096/utils/bazel/llvm-project-overlay/lld/BUILD.bazel#L71

Do you know what the difference is w/ your downstream use case that including that file directly doesn't work?

That said, this seems like a step in the right direction anyway.

https://github.com/llvm/llvm-project/pull/86363