Revert "[CIR] Fix warning in CIRGenAction.cpp (llvm#118389)"

This reverts commit eaa4eb2.

Author: lanza

clang/lib/CIR/FrontendAction/CIRGenAction.cpp

@@ -66,6 +66,9 @@ class CIRGenConsumer : public clang::ASTConsumer {
         MlirModule->print(*OutputStream, Flags);
       }
       break;
+    default:
+      llvm_unreachable("NYI: CIRGenAction other than EmitCIR");
+      break;
     }
   }
 };