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

[via cfe-commits]

zmodem wrote:

I was able to confirm on a local Mac that removing the `if(CLANG_PLUGIN_SUPPORT)` fixes the test, so I'll go ahead and commit that.

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