[llvm] [llvm][Tablegen][llvm-tblgen] Added keyword #undef to llvm-tblgen (PR #69135)

[Jessica Clarke via llvm-commits]

jrtc27 wrote:

I agree with you and would prefer you keep it open rather than close it because of one objection. I disagree with Mehdi's view of how include should work, and that we must forbid people from doing potentially-useful things.

https://github.com/llvm/llvm-project/pull/69135