[Clang] Add test dependency on llvm-ar

Following clang driver tests invoke llvm-ar, so ensure that
check-clang rebuilds llvm-ar.

 * test/Driver/clang-offload-bundler.c
 * test/Driver/hip-link-save-temps.hip
 * test/Driver/hip-link-static-library.hip
 * test/Driver/hip-toolchain-rdc-static-lib.hip

Differential Revision: https://reviews.llvm.org/D105285