[libc] Ensure that the required clang tools are up-to-date for libc GPU

The `clang-offload-packager`. `nvptx-arch`, and `amdgpu-arch` tools are
required for building the GPU target of `libc`. This patch ensures that
we build this tool when directly building `libc` via `ninja libc` or similar.

Reviewed By: tra

Differential Revision: https://reviews.llvm.org/D147581