[clang] [CIR] Disable CIR pipeline for LLVM IR inputs (PR #187729)

[Jan Leyonberg via cfe-commits]

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+// Verify that -fclangir is always forwarded to -cc1 by the driver, and
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jsjodin wrote:

I was thinking it might be better to keep all CIR in the same place until we want to integrate. If the CIR tests closely follow the clang test directory structure it should be easy to move them later on.

https://github.com/llvm/llvm-project/pull/187729