[clang] [CIR] Route MLIR diagnostics through clang::DiagnosticsEngine (PR #199297)

[Erich Keane via cfe-commits]

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@@ -519,4 +519,11 @@ def err_cir_to_cir_transform_failed : Error<
 def err_cir_verification_failed_pre_passes : Error<
     "CIR module verification error before running CIR-to-CIR passes">,
     DefaultFatal;
+
+// Diagnostics relayed from MLIR-side passes/verifier through the
+// clang::DiagnosticsEngine. The full message text comes from MLIR.
+def err_cir_mlir_diagnostic    : Error<"%0">;
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erichkeane wrote:

I could live with this, it is at least a move in the correct direction.

https://github.com/llvm/llvm-project/pull/199297