Add a `bzl_library` target for `toolchain_utils.bzl`

Now that `toolchain_utils.bzl` loads other bzl files, this will be helpful for downstream tests that rely on this file.

PiperOrigin-RevId: 633436595
Change-Id: Ia9cbd6c200e5d526e7c860d268506b0b05fc6207
1 file changed