[CIR] Minimize dependencies of check-clang-cir (#227957)
This adds special handling for the CIR test directories so that they
depend only on the components needed to run those tests. The goal of
this is to minimize what needs to be built to verify that MLIR changes
haven't broken CIR. There is no need to run the full set of Clang tests
to verify an MLIR change, since only CIR depends on MLIR.
Assisted-by: Cursor / various models
