[llvm] [mlir] [NFC][TableGen] Migrate IfDef/Namespace emitter from MLIR to LLVM (PR #161744)

[Mehdi Amini via llvm-commits]

joker-eph wrote:

>  Note that td lit tests also exercise this.

Since you're moving this to LLVM, I don't think there are existing lit tests exercising this, and I don't see any one added/moved in this PR, can you point me to the test coverage in LLVM?

https://github.com/llvm/llvm-project/pull/161744