[clang] [clang-repl] Lay the foundation of pretty printing for C. (PR #89811)

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zmodem wrote:

> Would dropping this conditional make it work for your case?

I don't have a mac handy to try it right now. If you commit it, our system will test it automatically :) Or maybe @thakis could give it a try?

https://github.com/llvm/llvm-project/pull/89811