[clang] [clang][CIR] Route .cir cc1 input to the ClangIR frontend action (PR #227156)

[Erich Keane via cfe-commits]

https://github.com/erichkeane approved this pull request.

This seems reasonable to me, though I don'ts see : are we making sure that this still compiles right even without clangir enabled? 

https://github.com/llvm/llvm-project/pull/227156