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

[Erich Keane via cfe-commits]

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+// RUN: %clang_cc1 -triple x86_64-unknown-linux-gnu -fclangir -emit-cir %s
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erichkeane wrote:

Would still like this to 'pipe' to filecheck.  In addition to 'not crash', it would be worthwhile to ensure we emit sensible IR.

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