[clang] [CIR] Build out AST consumer patterns to reach the entry point into CIRGen (PR #91007)

[Bruno Cardoso Lopes via cfe-commits]

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@@ -42,6 +47,14 @@ CreateFrontendBaseAction(CompilerInstance &CI) {
   StringRef Action("unknown");
   (void)Action;
 
+  auto UseCIR = CI.getFrontendOpts().UseClangIRPipeline;
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bcardosolopes wrote:

Right, it's a different discussion than naming. @joker-eph: what's the `auto` policy for MLIR, is it different from LLVM/Clang? I'm also having trouble to find the previous discussions, let me search a bit more.

https://github.com/llvm/llvm-project/pull/91007