[flang-commits] [flang] [flang] [mlir] Avoid clobbering mlir-tblgen target by defining dummy imported targets (PR #150987)

[Slava Zakharin via flang-commits]

vzakhari wrote:

I suppose the same issue will arise if someone tries to build just `mlir` (without `flang`) with a Nix sandbox, so it seems it is worth a more general fix for `mlir`.  I must admit, I still do not understand what happens in your build process, so I hope a more general `mlir` fix will attract reviewers who understand this change.

https://github.com/llvm/llvm-project/pull/150987